Microfabricated elastomeric valve and pump systems

ABSTRACT

A method of fabricating an elastomeric structure, comprising: forming a first elastomeric layer on top of a first micromachined mold, the first micromachined mold having a first raised protrusion which forms a first recess extending along a bottom surface of the first elastomeric layer; forming a second elastomeric layer on top of a second micromachined mold, the second micromachined mold having a second raised protrusion which forms a second recess extending along a bottom surface of the second elastomeric layer; bonding the bottom surface of the second elastomeric layer onto a top surface of the first elastomeric layer such that a control channel forms in the second recess between the first and second elastomeric layers; and positioning the first elastomeric layer on top of a planar substrate such that a flow channel forms in the first recess between the first elastomeric layer and the planar substrate.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This is a continuation of U.S. nonprovisional patent applicationSer. No. 09/605,520 filed Jun. 27, 2000. This nonprovisional patentapplication also claims the benefit of the following previously filedU.S. provisional patent application No. 60/186,856 filed Mar. 3, 2000.The text of these prior patent applications is hereby incorporated byreference. The text of concurrently filed PCT Application No.PCT/US00/17740 filed Jun. 27, 2000 is also hereby incorporated byreference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

[0002] Work described herein has been supported, in part, by NationalInstitute of Health grant HG-01642-02. The United States Government maytherefore have certain rights in the invention.

TECHNICAL FIELD

[0003] The present invention relates to microfabricated structures andmethods for producing microfabricated structures, and to microfabricatedsystems for regulating fluidflow.

BACKGROUND OF THE INVENTION

[0004] Various approaches to designing micro-fluidic pumps and valveshave been attempted. Unfortunately, each of these approaches suffersfrom its own limitations.

[0005] The two most common methods of producing microelectromechanical(MEMS) structures such as pumps and valves are silicon-based bulkmicro-machining (which is a subtractive fabrication method wherebysingle crystal silicon is lithographically patterned and then etched toform three-dimensional structures), and surface micro-machining (whichis an additive method where layers of semiconductor-type materials suchas polysilicon, silicon nitride, silicon dioxide, and various metals aresequentially added and patterned to make three-dimensional structures).

[0006] A limitation of the first approach of silicon-basedmicro-machining is that the stiffness of the semiconductor materialsused necessitates high actuation forces, which in turn result in largeand complex designs. In fact, both bulk and surface micro-machiningmethods are limited by the stiffness of the materials used. In addition,adhesion between various layers of the fabricated device is also aproblem. For example, in bulk micro-machining, wafer bonding techniquesmust be employed to create multilayer structures. On the other hand,when surface micro-machining, thermal stresses between the variouslayers of the device limits the total device thickness, often toapproximately 20 microns. Using either of the above methods, clean roomfabrication and careful quality control are required.

SUMMARY OF THE INVENTION

[0007] The present invention sets forth systems for fabricating andoperating microfabricated structures such as on/off valves, switchingvalves, and pumps e.g. made out of various layers of elastomer bondedtogether. The present structures and methods are ideally suited forcontrolling and channeling fluid movement, but are not so limited.

[0008] In a preferred aspect, the present invention uses a multilayersoft lithography process to build integrated (i.e.: monolithic)microfabricated elastomeric structures.

[0009] Advantages of fabricating the present structures by bindingtogether layers of soft elastomeric materials include the fact that theresulting devices are reduced by more than two orders of magnitude insize as compared to silicon-based devices. Further advantages of rapidprototyping, ease of fabrication, and biocompatability are alsoachieved.

[0010] In preferred aspects of the invention, separate elastomericlayers are fabricated on top of micromachined molds such that recessesare formed in each of the various elastomeric layers. By bonding thesevarious elastomeric layers together, the recesses extending along thevarious elastomeric layers form flow channels and control lines throughthe resulting monolithic, integral elastomeric structure. In variousaspects of the invention, these flow channels and control lines whichare formed in the elastomeric structure can be actuated to function asmicro-pumps and micro-valves, as will be explained.

[0011] In further optional aspects of the invention, the monolithicelastomeric structure is sealed onto the top of a planar substrate, withflow channels being formed between the surface of the planar substrateand the recesses which extend along the bottom surface of theelastomeric structure.

[0012] In one preferred aspect, the present monolithic elastomericstructures are constructed by bonding together two separate layers ofelastomer with each layer first being separately cast from arnicromachined mold. Preferably, the elastomer used is a two-componentaddition cure material in which the bottom elastomeric layer has anexcess of one component, while the top elastomeric layer has an excessof another component. In an exemplary embodiment, the elastomer used issilicone rubber. Two layers of elastomer are cured separately. Eachlayer is separately cured before the top layer is positioned on thebottom layer. The two layers are then bonded together. Each layerpreferably has an excess of one of the two components, such thatreactive molecules remain at the interface between the layers. The toplayer is assembled on top of the bottom layer and heated. The two layersbond irreversibly such that the strength of the interface approaches orequals the strength of the bulk elastomer. This creates a monolithicthree-dimensional patterned structure composed entirely of two layers ofbonded together elastomer. Additional layers may be added by simplyrepeating the process, wherein new layers, each having a layer ofopposite “polarity” are cured, and thereby bonded together.

[0013] In a second preferred aspect, a first photoresist layer isdeposited on top of a first elastomeric layer. The first photoresistlayer is then patterned to leave a line or pattern of lines ofphotoresist on the top surface of the first elastomeric layer. Anotherlayer of elastomer is then added and cured, encapsulating the line orpattern of lines of photoresist. A second photoresist layer is added andpatterned, and another layer of elastomer added and cured, leaving lineand patterns of lines of photoresist encapsulated in a monolithicelastomer structure. This process may be repeated to add moreencapsulated patterns and elastomer layers. Thereafter, the photoresistis removed leaving flow channel(s) and control line(s) in the spaceswhich had been occupied by the photoresist. This process may be repeatedto create elastomer structures having a multitude of layers.

[0014] An advantage of patterning moderate sized features (>/=10microns) using a photoresist method is that a high resolutiontransparency film can be used as a contact mask. This allows a singleresearcher to design, print, pattern the mold, and create a new set ofcast elastomer devices, typically all within 24 hours.

[0015] A further advantage of either above embodiment of the presentinvention is that due to its monolithic or integral nature, (i.e., allthe layers are composed of the same material) is that interlayeradhesion failures and thermal stress problems are completely avoided.

[0016] Further advantages of the present invention's preferred use of asilicone rubber or elastomer such as RTV 615 manufactured by GeneralElectric, is that it is transparent to visible light, making amultilayer optical trains possible, thereby allowing opticalinterrogation of various channels or chambers in the microfluidicdevice. As appropriately shaped elastomer layers can serve as lenses andoptical elements, bonding of layers allows the creation of multilayeroptical trains. In addition, GE RTV 615 elastomer is biocompatible.Being soft, closed valves form a good seal even if there are smallparticulates in the flow channel. Silicone rubber is also bio-compatibleand inexpensive, especially when compared with a single crystal silicon.

[0017] Monolithic elastomeric valves and pumps also avoid many of thepractical problems affecting flow systems based on electro-osmotic flow.Typically, electro-osmotic flow systems suffer from bubble formationaround the electrodes and the flow is strongly dependent on thecomposition of the flow medium. Bubble formation seriously restricts theuse of electro-osmotic flow in microfluidic devices, making it difficultto construct functioning integrated devices. The magnitude of flow andeven its direction typically depends in a complex fashion on ionicstrength and type, the presence of surfactants and the charge on thewalls of the flow channel. Moreover, since electrolysis is taking placecontinuously, the eventual capacity of buffer to resist pH changes mayalso be reached. Furthermore, electro-osmotic flow always occurs incompetition with electrophoresis. As different molecules may havedifferent electrophoretic mobilities, unwanted electrophoreticseparation may occur in the electro-osmotic flow. Finally,electro-osmotic flow can not easily be used to stop flow, haltdiffusion, or to balance pressure differences.

[0018] A further advantage of the present monolithic elastomeric valveand pump structures are that they can be actuated at very high speeds.For example, the present inventors have achieved a response time for avalve with aqueous solution therein on the order of one millisecond,such that the valve opens and closes at speeds approaching or exceeding100 Hz. In particular, a non-exclusive list of ranges of cycling speedsfor the opening and closing of the valve structure include between about0.001 and 10000 ms, between about 0.01 and 1000 ms, between about 0.1and 100 ms, and between about 1 and 10 ms. The cycling speeds dependupon the composition and structure of a valve used for a particularapplication and the method of actuation, and thus cycling speeds outsideof the listed ranges would fall within the scope of the presentinvention.

[0019] Further advantages of the present pumps and valves are that theirsmall size makes them fast and their softness contributes to making themdurable. Moreover, as they close linearly with differential appliedpressure, this linear relationship allows fluid metering and valveclosing in spite of high back pressures.

[0020] In various aspects of the invention, a plurality of flow channelspass through the elastomeric structure with a second flow channelextending across and above a first flow channel. In this aspect of theinvention, a thin membrane of elastomer separates the first and secondflow channels. As will be explained, downward movement of this membrane(due to the second flow channel being pressurized or the membrane beingotherwise actuated) will cut off flow passing through the lower flowchannel.

[0021] In optional preferred aspects of the present systems, a pluralityof individually addressable valves are formed connected together in anelastomeric structure and are then activated in sequence such thatperistaltic pumping is achieved. More complex systems includingnetworked or multiplexed control systems, selectably addressable valvesdisposed in a grid of valves, networked or multiplexed reaction chambersystems and biopolymer synthesis systems are also described.

[0022] One embodiment of a microfabricated elastomeric structure inaccordance with the present invention comprises an elastomeric blockformed with first and second microfabricated recesses therein, a portionof the elastomeric block deflectable when the portion is actuated.

[0023] One embodiment of a method of microfabricating an elastomericstructure comprises the steps of microfabricating a first elastomericlayer, microfabricating a second elastomeric layer; positioning thesecond elastomeric layer on top of the first elastomeric layer, andbonding a bottom surface of the second elastomeric layer onto a topsurface of the first elastomeric layer.

[0024] A first alternative embodiment of a method of microfabricating anelastomeric structure comprises the steps of forming a first elastomericlayer on top of a first micromachined mold, the first micromachined moldhaving at least one first raised protrusion which forms at least onefirst channel in the bottom surface of the first elastomeric layer. Asecond elastomeric layer is formed on top of a second micromachinedmold, the second micromachined mold having at least one second raisedprotrusion which forms at least one second channel in the bottom surfaceof the second elastomeric layer. The bottom surface of the secondelastomeric layer is bonded onto a top surface of the first elastomericlayer such that the at least one second channel is enclosed between thefirst and second elastomeric layers.

[0025] A second alternative embodiment of a method of microfabricatingan elastomeric structure in accordance with the present inventioncomprises the steps of forming a first elastomeric layer on top of asubstrate, curing the first elastomeric layer, and depositing a firstsacrificial layer on the top surface of the first elastomeric layer. Aportion of the first sacrificial layer is removed such that a firstpattern of sacrificial material remains on the top surface of the firstelastomeric layer. A second elastomeric layer is formed over the firstelastomeric layer thereby encapsulating the first pattern of sacrificialmaterial between the first and second elastomeric layers. The secondelastomeric layer is cured and then sacrificial material is removedthereby forming at least one first recess between the first and secondlayers of elastomer.

[0026] An embodiment of a method of actuating an elastomeric structurein accordance with the present invention comprises providing anelastomeric block formed with first and second microfabricated recessestherein, the first and second microfabricated recesses being separatedby a portion of the structure which is deflectable into either of thefirst or second recesses when the other of the first and secondrecesses. One of the recesses is pressurized such that the portion ofthe elastomeric structure separating the second recess from the firstrecess is deflected into the other of the two recesses.

[0027] In other optional preferred aspects, magnetic or conductivematerials can be added to make layers of the elastomer magnetic orelectrically conducting, thus enabling the creation of all elastomerelectromagnetic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Part I

[0029] FIGS. 1 to 7A illustrate successive steps of a first method offabricating the present invention, as follows:

[0030]FIG. 1 is an illustration of a first elastomeric layer formed ontop of a micromachined mold.

[0031]FIG. 2 is an illustration of a second elastomeric layer formed ontop of a micromachined mold.

[0032]FIG. 3 is an illustration of the elastomeric layer of FIG. 2removed from the micromachined mold and positioned over the top of theelastomeric layer of FIG. 1

[0033]FIG. 4 is an illustration corresponding to FIG. 3, but showing thesecond elastomeric layer positioned on top of the first elastomericlayer.

[0034]FIG. 5 is an illustration corresponding to FIG. 4, but showing thefirst and second elastomeric layers bonded together.

[0035]FIG. 6 is an illustration corresponding to FIG. 5, but showing thefirst micromachine mold removed and a planar substrate positioned in itsplace.

[0036]FIG. 7A is an illustration corresponding to FIG. 6, but showingthe elastomeric structure sealed onto the planar substrate.

[0037]FIGS. 7B is a front sectional view corresponding to FIG. 7A,showing an open flow channel.

[0038] FIGS. 7C-7G are illustrations showing steps of a method forforming an elastomeric structure having a membrane formed from aseparate elastomeric layer.

[0039] Part II

[0040]FIG. 7H show the closing of a first flow channel by pressurizing asecond flow channel, as follows:

[0041]FIG. 7H corresponds to FIG. 7A, but shows a first flow channelclosed by pressurization in second flow channel.

[0042] Part III

[0043] FIGS. 8 to 18 illustrate successive steps of a second method offabricating the present invention, as follows:

[0044]FIG. 8 is an illustration of a first elastomeric layer depositedon a planar substrate.

[0045]FIG. 9 is an illustration showing a first photoresist layerdeposited on top of the first elastomeric layer of FIG. 8.

[0046]FIG. 10 is an illustration showing the system of FIG. 9, but witha portion of the first photoresist layer removed, leaving only a firstline of photoresist.

[0047]FIG. 11 is an illustration showing a second elastomeric layerapplied on top of the first elastomeric layer over the first line ofphotoresist of FIG. 10, thereby encasing the photoresist between thefirst and second elastomeric layers.

[0048]FIG. 12 corresponds to FIG. 11, but shows the integratedmonolithic structure produced after the first and second elastomerlayers have been bonded together.

[0049]FIG. 13 is an illustration showing a second photoresist layerdeposited on top of the integral elastomeric structure of FIG. 12.

[0050]FIG. 14 is an illustration showing the system of FIG. 13, but witha portion of the second photoresist layer removed, leaving only a secondline of photoresist.

[0051]FIG. 15 is an illustration showing a third elastomer layer appliedon top of the second elastomeric layer and over the second line ofphotoresist of FIG. 14, thereby encapsulating the second line ofphotoresist between the elastomeric structure of FIG. 12 and the thirdelastomeric layer.

[0052]FIG. 16 corresponds to FIG. 15, but shows the third elastomericlayer cured so as to be bonded to the monolithic structure composed ofthe previously bonded first and second elastomer layers.

[0053]FIG. 17 corresponds to FIG. 16, but shows the first and secondlines of photoresist removed so as to provide two perpendicularoverlapping, but not intersecting, flow channels passing through theintegrated elastomeric structure.

[0054]FIG. 18 is an illustration showing the system of FIG. 17, but withthe planar substrate thereunder removed.

[0055] Part IV

[0056]FIGS. 19 and 20 show further details of different flow channelcross-sections, as follows:

[0057]FIG. 19 shows a rectangular cross-section of a first flow channel.

[0058]FIG. 20 shows the flow channel cross section having a curved uppersurface.

[0059] Part V

[0060] FIGS. 21 to 24 show experimental results achieved by preferredembodiments of the present microfabricated valve:

[0061]FIG. 21 illustrates valve opening vs. applied pressure for variousflow channels.

[0062]FIG. 22 illustrates time response of a 100 μm×100 μm×10 μm RTVmicrovalve.

[0063] Part VI

[0064]FIGS. 23A to 33 show various microfabricated structures, networkedtogether according to aspects of the present invention:

[0065]FIG. 23A is a top schematic view of an on/off valve.

[0066]FIG. 23B is a sectional elevation view along line 23B-23B in FIG.23A

[0067]FIG. 24 is a top schematic view of a peristaltic pumping system.

[0068]FIG. 24B is a sectional elevation view along line 24B-24B in FIG.24A

[0069]FIG. 25 is a graph showing experimentally achieved pumping ratesvs. frequency for an embodiment of the peristaltic pumping system ofFIG. 24.

[0070]FIG. 26A is a top schematic view of one control line actuatingmultiple flow lines simultaneously.

[0071]FIG. 26B is a sectional elevation view along line 26B-26B in FIG.26A

[0072]FIG. 27 is a schematic illustration of a multiplexed systemadapted to permit flow through various channels.

[0073]FIG. 28A is a plan view of a flow layer of an addressable reactionchamber structure.

[0074]FIG. 28B is a bottom plan view of a control channel layer of anaddressable reaction chamber structure.

[0075]FIG. 28C is an exploded perspective view of the addressablereaction chamber structure formed by bonding the control channel layerof FIG. 28B to the top of the flow layer of FIG. 28A.

[0076]FIG. 28D is a sectional elevation view corresponding to FIG. 28C,taken along line 28D-28D in FIG. 28C.

[0077]FIG. 29 is a schematic of a system adapted to selectively directfluid flow into any of an array of reaction wells.

[0078]FIG. 30 is a schematic of a system adapted for selectable lateralflow between parallel flow channels.

[0079]FIG. 31A is a bottom plan view of first layer (i.e.: the flowchannel layer) of elastomer of a switchable flow array.

[0080]FIG. 31B is a bottom plan view of a control channel layer of aswitchable flow array.

[0081]FIG. 31C shows the alignment of the first layer of elastomer ofFIG. 31A with one set of control channels in the second layer ofelastomer of FIG. 31B.

[0082]FIG. 31D also shows the alignment of the first layer of elastomerof FIG. 31A with the other set of control channels in the second layerof elastomer of FIG. 31B.

[0083]FIG. 32 is a schematic of an integrated system for biopolymersynthesis.

[0084]FIG. 33 is a schematic of a further integrated system forbiopolymer synthesis.

[0085]FIG. 34 is an optical micrograph of a section of a test structurehaving seven layers of elastomer bonded together.

[0086] FIGS. 35A-35D show the steps of one embodiment of a method forfabricating an elastomer layer having a vertical via formed therein.

[0087]FIG. 36 shows one embodiment of a sorting apparatus in accordancewith the present invention.

[0088]FIG. 37 shows an embodiment of an apparatus for flowing processgases over a semiconductor wafer in accordance with the presentinvention.

[0089]FIG. 38 shows an exploded view of one embodiment of a micro-mirrorarray structure in accordance with the present invention.

[0090]FIG. 39 shows a perspective view of a first embodiment of arefractive device in accordance with the present invention.

[0091]FIG. 40 shows a perspective view of a second embodiment of arefractive device in accordance with the present invention.

[0092]FIG. 41 shows a perspective view of a third embodiment of arefractive device in accordance with the present invention.

[0093] FIGS. 42A-42J show views of one embodiment of a normally-closedvalve structure in accordance with the present invention.

[0094] FIGS. 43 shows a plan view of one embodiment of a device forperforming separations in accordance with the present invention.

[0095] FIGS. 44A-44D show plan views illustrating operation of oneembodiment of a cell pen structure in accordance with the presentinvention.

[0096] FIGS. 45A-45B show plan and cross-sectional views illustratingoperation of one embodiment of a cell cage structure in accordance withthe present invention.

[0097] FIGS. 46A-46B show cross-sectional views illustrating operationof one embodiment of a cell grinder structure in accordance with thepresent invention.

[0098]FIG. 47 shows a plan view of one embodiment of a pressureoscillator structure in accordance with the present invention.

[0099]FIGS. 48A and 48B show plan views illustrating operation of oneembodiment of a side-actuated valve structure in accordance with thepresent invention.

[0100]FIG. 49 plots Young's modulus versus percentage dilution of GE RTV615 elastomer with GE SF96-50 silicone fluid.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0101] The present invention comprises a variety of microfabricatedelastomeric structures which may be used as pumps or valves. Methods offabricating the preferred elastomeric structures are also set forth.

[0102] Methods of Fabricating the Present Invention:

[0103] Two exemplary methods of fabricating the present invention areprovided herein. It is to be understood that the present invention isnot limited to fabrication by one or the other of these methods. Rather,other suitable methods of fabricating the present microstructures,including modifying the present methods, are also contemplated.

[0104] FIGS. 1 to 7B illustrate sequential steps of a first preferredmethod of fabricating the present microstructure, (which may be used asa pump or valve). FIGS. 8 to 18 illustrate sequential steps of a secondpreferred method of fabricating the present microstructure, (which alsomay be used as a pump or valve).

[0105] As will be explained, the preferred method of FIGS. 1 to 7Binvolves using pre-cured elastomer layers which are assembled andbonded. Conversely, the preferred method of FIGS. 8 to 18 involvescuring each layer of elastomer “in place”. In the following description“channel” refers to a recess in the elastomeric structure which cancontain a flow of fluid or gas.

[0106] The First Exemplary Method:

[0107] Referring to FIG. 1, a first micro-machined mold 10 is provided.Micro-machined mold 10 may be fabricated by a number of conventionalsilicon processing methods, including but not limited tophotolithography, ion-milling, and electron beam lithography.

[0108] As can be seen, micro-machined mold 10 has a raised line orprotrusion 11 extending therealong. A first elastomeric layer 20 is caston top of mold 10 such that a first recess 21 will be formed in thebottom surface of elastomeric layer 20, (recess 21 corresponding indimension to protrusion 11), as shown.

[0109] As can be seen in FIG. 2, a second micro-machined mold 12 havinga raised protrusion 13 extending therealong is also provided. A secondelastomeric layer 22 is cast on top of mold 12, as shown, such that arecess 23 will be formed in its bottom surface corresponding to thedimensions of protrusion 13.

[0110] As can be seen in the sequential steps illustrated in FIGS. 3 and4, second elastomeric layer 22 is then removed from mold 12 and placedon top of first elastomeric layer 20. As can be seen, recess 23extending along the bottom surface of second elastomeric layer 22 willform a flow channel 32.

[0111] Referring to FIG. 5, the separate first and second elastomericlayers 20 and 22 (FIG. 4) are then bonded together to form an integrated(i.e.: monolithic) elastomeric structure 24.

[0112] As can been seen in the sequential step of FIGS. 6 and 7A,elastomeric structure 24 is then removed from mold 10 and positioned ontop of a planar substrate 14. As can be seen in FIG. 7A and 7B, whenelastomeric structure 24 has been sealed at its bottom surface to planarsubstrate 14, recess 21 will form a flow channel 30.

[0113] The present elastomeric structures form a reversible hermeticseal with nearly any smooth planar substrate. An advantage to forming aseal this way is that the elastomeric structures may be peeled up,washed, and re-used. In preferred aspects, planar substrate 14 is glass.A further advantage of using glass is that glass is transparent,allowing optical interrogation of elastomer channels and reservoirs.Alternatively, the elastomeric structure may be bonded onto a flatelastomer layer by the same method as described above, forming apermanent and high-strength bond. This may prove advantageous whenhigher back pressures are used.

[0114] As can be seen in FIG. 7A and 7B, flow channels 30 and 32 arepreferably disposed at an angle to one another with a small membrane 25of substrate 24 separating the top of flow channel 30 from the bottom offlow channel 32.

[0115] In preferred aspects, planar substrate 14 is glass. An advantageof using glass is that the present elastomeric structures may be peeledup, washed and reused. A further advantage of using glass is thatoptical sensing may be employed. Alternatively, planar substrate 14 maybe an elastomer itself, which may prove advantageous when higher backpressures are used.

[0116] The method of fabrication just described may be varied to form astructure having a membrane composed of an elastomeric materialdifferent than that forming the walls of the channels of the device.This variant fabrication method is illustrated in FIGS. 7C-7G.

[0117] Referring to FIG. 7C, a first micro-machined mold 10 is provided.Micro-machined mold 10 has a raised line or protrusion 11 extendingtherealong. In FIG. 7D, first elastomeric layer 20 is cast on top offirst micro-machined mold 10 such that the top of the first elastomericlayer 20 is flush with the top of raised line or protrusion 11. This maybe accomplished by carefully controlling the volume of elastomericmaterial spun onto mold 10 relative to the known height of raised line11. Alternatively, the desired shape could be formed by injectionmolding.

[0118] In FIG. 7E, second micro-machined mold 12 having a raisedprotrusion 13 extending therealong is also provided. Second elastomericlayer 22 is cast on top of second mold 12 as shown, such that recess 23is formed in its bottom surface corresponding to the dimensions ofprotrusion 13.

[0119] In FIG. 7F, second elastomeric layer 22 is removed from mold 12and placed on top of third elastomeric layer 222. Second elastomericlayer 22 is bonded to third elastomeric layer 20 to form integralelastomeric block 224 using techniques described in detail below. Atthis point in the process, recess 23 formerly occupied by raised line 13will form flow channel 23.

[0120] In FIG. 7G, elastomeric block 224 is placed on top of firstmicro-machined mold 10 and first elastomeric layer 20. Elastomeric blockand first elastomeric layer 20 are then bonded together to form anintegrated (i.e.: monolithic) elastomeric structure 24 having a membranecomposed of a separate elastomeric layer 222.

[0121] When elastomeric structure 24 has been sealed at its bottomsurface to a planar substrate in the manner described above inconnection with FIG. 7A, the recess formerly occupied by raised line 11will form flow channel 30.

[0122] The variant fabrication method illustrated above in conjunctionwith FIGS. 7C-7G offers the advantage of permitting the membrane portionto be composed of a separate material than the elastomeric material ofthe remainder of the structure. This is important because the thicknessand elastic properties of the membrane play a key role in operation ofthe device. Moreover, this method allows the separate elastomer layer toreadily be subjected to conditioning prior to incorporation into theelastomer structure. As discussed in detail below, examples ofpotentially desirable condition include the introduction of magnetic orelectrically conducting species to permit actuation of the membrane,and/or the introduction of dopant into the membrane in order to alterits elasticity.

[0123] While the above method is illustrated in connection with formingvarious shaped elastomeric layers formed by replication molding on topof a micromachined mold, the present invention is not limited to thistechnique. Other techniques could be employed to form the individuallayers of shaped elastomeric material that are to be bonded together.For example, a shaped layer of elastomeric material could be formed bylaser cutting or injection molding, or by methods utilizing chemicaletching and/or sacrificial materials as discussed below in conjunctionwith the second exemplary method.

[0124] The Second Exemplary Method:

[0125] A second exemplary method of fabricating an elastomeric structurewhich may be used as a pump or valve is set forth in the sequentialsteps shown in FIGS. 8-18.

[0126] In this aspect of the invention, flow and control channels aredefined by first patterning photoresist on the surface of an elastomericlayer (or other substrate, which may include glass) leaving a raisedline photoresist where a channel is desired. Next, a second layer ofelastomer is added thereover and a second photoresist is patterned onthe second layer of elastomer leaving a raised line photoresist where achannel is desired. A third layer of elastomer is deposited thereover.Finally, the photoresist is removed by dissolving it out of theelastomer with an appropriate solvent, with the voids formed by removalof the photoresist becoming the flow channels passing through thesubstrate.

[0127] Referring first to FIG. 8, a planar substrate 40 is provided. Afirst elastomeric layer 42 is then deposited and cured on top of planarsubstrate 40. Referring to FIG. 9, a first photoresist layer 44A is thendeposited over the top of elastomeric layer 42. Referring to FIG. 10, aportion of photoresist layer 44A is removed such that only a first lineof photoresist 44B remains as shown. Referring to FIG. 11, a secondelastomeric layer 46 is then deposited over the top of first elastomericlayer 42 and over the first line of photoresist 44B as shown, therebyencasing first line of photoresist 44B between first elastomeric layer42 and second elastomeric layer 46. Referring to FIG. 12, elastomericlayers 46 is then cured on layer 42 to bond the layers together to forma monolithic elastomeric substrate 45.

[0128] Referring to FIG. 13, a second photoresist layer 48A is thendeposited over elastomeric structure 45. Referring to FIG. 14, a portionof second photoresist layer 48A is removed, leaving only a secondphotoresist line 48B on top of elastomeric structure 45 as shown.Referring to FIG. 15, a third elastomeric layer 50 is then depositedover the top of elastomeric structure 45 (comprised of secondelastomeric layer 42 and first line of photoresist 44B) and secondphotoresist line 48B as shown, thereby encasing the second line ofphotoresist 48B. between elastomeric structure 45 and third elastomericlayer 50.

[0129] Referring to FIG. 16, third elastomeric layer 50 and elastomericstructure 45 (comprising first elastomeric layer 42 and secondelastomeric layer 46 bonded together) is then bonded together forming amonolithic elastomeric structure 47 having photoresist lines 44B and 48Bpassing therethrough as shown. Referring to FIG. 17, photoresist lines44B, 48B are then removed (for example, by an solvent ) such that afirst flow channel 60 and a second flow channel 62 are provided in theirplace, passing through elastomeric structure 47 as shown. Lastly,referring to FIG. 18, planar substrate 40 can be removed from the bottomof the integrated monolithic structure.

[0130] The method described in FIGS. 8-18 fabricates a patternedelastomer structure utilizing development of photoresist encapsulatedwithin elastomer material. However, the methods in accordance with thepresent invention are not limited to utilizing photoresist. Othermaterials such as metals could also serve as sacrificial materials to beremoved selective to the surrounding elastomer material, and the methodwould remain within the scope of the present invention. For example, asdescribed in detail below in connection with FIGS. 35A-35D, gold metalmay be etched selective to RTV 615 elastomer utilizing the appropriatechemical mixture.

[0131] Preferred Layer and Channel Dimensions:

[0132] Microfabricated refers to the size of features of an elastomericstructure fabricated in accordance with an embodiment of the presentinvention. In general, variation in at least one dimension ofmicrofabricated structures is controlled to the micron level, with atleast one dimension being microscopic (i.e. below 1000 μm).Microfabrication typically involves semiconductor or MEMS fabricationtechniques such as photolithography and spincoating that are designedfor to produce feature dimensions on the microscopic level, with atleast some of the dimension of the microfabricated structure requiring amicroscope to reasonably resolve/image the structure.

[0133] In preferred aspects, flow channels 30, 32, 60 and 62 preferablyhave width-to-depth ratios of about 10:1. A non-exclusive list of otherranges of width-to-depth ratios in accordance with embodiments of thepresent invention is 0.1:1 to 100:1, more preferably 1:1 to 50:1, morepreferably 2:1 to 20:1, and most preferably 3:1 to 15:1. In an exemplaryaspect, flow channels 30, 32, 60 and 62 have widths of about 1 to 1000microns. A non-exclusive list of other ranges of widths of flow channelsin accordance with embodiments of the present invention is 0.01 to 1000microns, more preferably 0.05 to 1000 microns, more preferably 0.2 to500 microns, more preferably 1 to 250 microns, and most preferably 10 to200 microns. Exemplary channel widths include 0.1 μm, 1 μm, 2 μm, 5 μm,10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm,110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm,200 μm, 210 μm, 220 μm, 230 μm, 240 μm, and 250 μm.

[0134] Flow channels 30, 32, 60, and 62 have depths of about 1 to 100microns. A non-exclusive list of other ranges of depths of flow channelsin accordance with embodiments of the present invention is 0.01 to 1000microns, more preferably 0.05 to 500 microns, more preferably 0.2 to 250microns, and more preferably 1 to 100 microns, more preferably 2 to 20microns, and most preferably 5 to 10 microns. Exemplary channel depthsinclude including 0.01 μm, 0.02 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 1μm, 2 μm, 3 μm, 4 μm, 5 μm, 7.5 μm, 10 μm, 12.5 μm, 15 μm, 17.5 μm, 20μm, 22.5 μm, 25 μm, 30 μm, 40 μm, 50 μm, 75 μm, 100 μm, 150 μm, 200 μm,and 250 μm.

[0135] The flow channels are not limited to these specific dimensionranges and examples given above, and may vary in width in order toaffect the magnitude of force required to deflect the membrane asdiscussed at length below in conjunction with FIG. 27. For example,extremely narrow flow channels having a width on the order of 0.01 μmmay be useful in optical and other applications, as discussed in detailbelow. Elastomeric structures which include portions having channels ofeven greater width than described above are also contemplated by thepresent invention, and examples of applications of utilizing such widerflow channels include fluid reservoir and mixing channel structures.

[0136] Elastomeric layer 22 may be cast thick for mechanical stability.In an exemplary embodiment, layer 22 is 50 microns to severalcentimeters thick, and more preferably approximately 4 mm thick. Anon-exclusive list of ranges of thickness of the elastomer layer inaccordance with other embodiments of the present invention is betweenabout 0.1 micron to 10 cm, 1 micron to 5 cm, 10 microns to 2 cm, 100microns to 10 mm.

[0137] Accordingly, membrane 25 of FIG. 7B separating flow channels 30and 32 has a typical thickness of between about 0.01 and 1000 microns,more preferably 0.05 to 500 microns, more preferably 0.2 to 250, morepreferably 1 to 100 microns, more preferably 2 to 50 microns, and mostpreferably 5 to 40 microns. As such, the thickness of elastomeric layer22 is about 100 times the thickness of elastomeric layer 20. Exemplarymembrane thicknesses include 0.01 μm, 0.02 μm, 0.03 μm, 0.05 μm, 0.1 μm,0.2 μm, 0.3 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 5 μm, 7.5 μm, 10 μm, 12.5 μm,15 μm, 17.5 μm, 20 μm, 22.5 μm, 25 μm, 30 μm, 40 μm, 50 μm, 75 μm, 100μm, 150 μm, 200 μm, 250 μm, 300 μm, 400 μm, 500 μm, 750 μm, and 1000 μmSimilarly, first elastomeric layer 42 may have a preferred thicknessabout equal to that of elastomeric layer 20 or 22; second elastomericlayer 46 may have a preferred thickness about equal to that ofelastomeric layer 20; and third elastomeric layer 50 may have apreferred thickness about equal to that of elastomeric layer 22.

[0138] Multilayer Soft Lithography Construction Techniques andMaterials:

[0139] Soft Lithographic Bonding:

[0140] Preferably, elastomeric layers 20 and 22 (or elastomeric layers42, 46 and 50) are bonded together chemically, using chemistry that isintrinsic to the polymers comprising the patterned elastomer layers.Most preferably, the bonding comprises two component “addition cure”bonding.

[0141] In a preferred aspect, the various layers of elastomer are boundtogether in a heterogenous bonding in which the layers have a differentchemistry. Alternatively, a homogenous bonding may be used in which alllayers would be of the same chemistry. Thirdly, the respective elastomerlayers may optionally be glued together by an adhesive instead. In afourth aspect, the elastomeric layers may be thermoset elastomers bondedtogether by heating.

[0142] In one aspect of homogeneous bonding, the elastomeric layers arecomposed of the same elastomer material, with the same chemical entityin one layer reacting with the same chemical entity in the other layerto bond the layers together, In one embodiment, bonding between polymerchains of like elastomer layers may result from activation of acrosslinking agent due to light, heat, or chemical reaction with aseparate chemical species.

[0143] Alternatively in a heterogeneous aspect, the elastomeric layersare composed of different elastomeric materials, with a first chemicalentity in one layer reacting with a second chemical entity in anotherlayer. In one exemplary heterogenous aspect, the bonding process used tobind respective elastomeric layers together may comprise bondingtogether two layers of RTV 615 silicone. RTV 615 silicone is a two-partaddition-cure silicone rubber. Part A contains vinyl groups andcatalyst; part B contains silicon hydride (Si—H) groups. Theconventional ratio for RTV 615 is 10A:1B. For bonding, one layer may bemade with 30A:1B (i.e. excess vinyl groups) and the other with 3A:1B(i.e. excess Si—H groups). Each layer is cured separately. When the twolayers are brought into contact and heated at elevated temperature, theybond irreversibly forming a monolithic elastomeric substrate.

[0144] In an exemplary aspect of the present invention, elastomericstructures are formed utilizing Sylgard 182, 184 or 186, or aliphaticurethane diacrylates such as (but not limited to) Ebecryl 270 or Irr 245from UCB Chemical.

[0145] In one embodiment in accordance with the present invention,two-layer elastomeric structures were fabricated from pure acrylatedUrethane Ebe 270. A thin bottom layer was spin coated at 8000 rpm for 15seconds at 170° C. The top and bottom layers were initially cured underultraviolet light for 10 minutes under nitrogen utilizing a Model ELC500 device manufactured by Electrolite corporation. The assembled layerswere then cured for an additional 30 minutes. Reaction was catalyzed bya 0.5% vol/vol mixture of Irgacure 500 manufactured by Ciba-GeigyChemicals. The resulting elastomeric material exhibited moderateelasticity and adhesion to glass.

[0146] In another embodiment in accordance with the present invention,two-layer elastomeric structures were fabricated from a combination of25% Ebe 270/50% Irr245/25% isopropyl alcohol for a thin bottom layer,and pure acrylated Urethane Ebe 270 as a top layer. The thin bottomlayer was initially cured for 5 min, and the top layer initially curedfor 10 minutes, under ultraviolet light under nitrogen utilizing a ModelELC 500 device manufactured by Electrolite corporation. The assembledlayers were then cured for an additional 30 minutes. Reaction wascatalyzed by a 0.5% vol/vol mixture of Irgacure 500 manufactured byCiba-Geigy Chemicals. The resulting elastomeric material exhibitedmoderate elasticity and adhered to glass.

[0147] Alternatively, other bonding methods may be used, includingactivating the elastomer surface, for example by plasma exposure, sothat the elastomer layers/substrate will bond when placed in contact.For example, one possible approach to bonding together elastomer layerscomposed of the same material is set forth by Duffy et al, “RapidPrototyping of Microfluidic Systems in Poly (dimethylsiloxane)”,Analytical Chemistry (1998), 70, 4974-4984, incorporated herein byreference. This paper discusses that exposing polydimethylsiloxane(PDMS) layers to oxygen plasma causes oxidation of the surface, withirreversible bonding occurring when the two oxidized layers are placedinto contact.

[0148] Yet another approach to bonding together successive layers ofelastomer is to utilize the adhesive properties of uncured elastomer.Specifically, a thin layer of uncured elastomer such as RTV 615 isapplied on top of a first cured elastomeric layer. Next, a second curedelastomeric layer is placed on top of the uncured elastomeric layer. Thethin middle layer of uncured elastomer is then cured to produce amonolithic elastomeric structure. Alternatively, uncured elastomer canbe applied to the bottom of a first cured elastomer layer, with thefirst cured elastomer layer placed on top of a second cured elastomerlayer. Curing the middle thin elastomer layer again results in formationof a monolithic elastomeric structure.

[0149] Where encapsulation of sacrificial layers is employed tofabricate the elastomer structure as described above in FIGS. 8-18,bonding of successive elastomeric layers may be accomplished by pouringuncured elastomer over a previously cured elastomeric layer and anysacrificial material patterned thereupon. Bonding between elastomerlayers occurs due to interpenetration and reaction of the polymer chainsof an uncured elastomer layer with the polymer chains of a curedelastomer layer. Subsequent curing of the elastomeric layer will createa bond between the elastomeric layers and create a monolithicelastomeric structure.

[0150] Referring to the first method of FIGS. 1 to 7B, first elastomericlayer 20 may be created by spin-coating an RTV mixture onmicrofabricated mold 12 at 2000 rpm's for 30 seconds yielding athickness of approximately 40 microns. Second elastomeric layer 22 maybe created by spin-coating an RTV mixture on microfabricated mold 11.Both layers 20 and 22 may be separately baked or cured at about 80° C.for 1.5 hours. The second elastomeric layer 22 may be bonded onto firstelastomeric layer 20 at about 80° C. for about 1.5 hours.

[0151] Micromachined molds 10 and 12 may be patterned photoresist onsilicon wafers. In an exemplary aspect, a Shipley SJR 5740 photoresistwas spun at 2000 rpm patterned with a high resolution transparency filmas a mask and then developed yielding an inverse channel ofapproximately 10 microns in height. When baked at approximately 200° C.for about 30 minutes, the photoresist reflows and the inverse channelsbecome rounded. In preferred aspects, the molds may be treated withtrimethylchlorosilane (TMCS) vapor for about a minute before each use inorder to prevent adhesion of silicone rubber.

[0152] Using the various multilayer soft lithography constructiontechniques and materials set forth herein, the present inventors haveexperimentally succeeded in creating channel networks comprises of up toseven separate elastomeric layers thick, with each layer being about 40μm thick. It is foreseeable that devices comprising more than sevenseparate elastomeric layers bonded together could be developed.

[0153] Suitable Elastomeric Materials:

[0154] Allcock et al, Contemporary Polymer Chemistry, 2nd Ed. describeselastomers in general as polymers existing at a temperature betweentheir glass transistion temperature and liquefaction temperature.Elastomeric materials exhibit elastic properties because the polymerchains readily undergo torsional motion to permit uncoiling of thebackbone chains in response to a force, with the backbone chainsrecoiling to assume the prior shape in the absence of the force. Ingeneral, elastomers deform when force is applied, but then return totheir original shape when the force is removed. The elasticity exhibitedby elastomeric materials may be characterized by a Young's modulus.Elastomeric materials having a Young's modulus of between about 1 Pa-1TPa, more preferably between about 10 Pa-100 GPa, more preferablybetween about 20 Pa-1 GPa, more preferably between about 50 Pa-10 MPa,and more preferably between about 100 Pa-1 MPa are useful in accordancewith the present invention, although elastomeric materials having aYoung's modulus outside of these ranges could also be utilized dependingupon the needs of a particular application.

[0155] The systems of the present invention may be fabricated from awide variety of elastomers. In an exemplary aspect, elastomeric layers20, 22, 42, 46 and 50 may preferably be fabricated from silicone rubber.However, other suitable elastomers may also be used.

[0156] In an exemplary aspect of the present invention, the presentsystems are fabricated from an elastomeric polymer such as GE RTV 615(formulation), a vinylsilane crosslinked (type) silicone elastomer(family). However, the present systems are not limited to this oneformulation, type or even this family of polymer; rather, nearly anyelastomeric polymer is suitable. An important requirement for thepreferred method of fabrication of the present microvalves is theability to bond multiple layers of elastomers together. In the case ofmultilayer soft lithography, layers of elastomer are cured separatelyand then bonded together. This scheme requires that cured layers possesssufficient reactivity to bond together. Either the layers may be of thesame type, and are capable of bonding to themselves, or they may be oftwo different types, and are capable of bonding to each other. Otherpossibilities include the use an adhesive between layers and the use ofthermoset elastomers.

[0157] Given the tremendous diversity of polymer chemistries,precursors, synthetic methods, reaction conditions, and potentialadditives, there are a huge number of possible elastomer systems thatcould be used to make monolithic elastomeric microvalves and pumps.Variations in the materials used will most likely be driven by the needfor particular material properties, i.e. solvent resistance, stiffness,gas permeability, or temperature stability.

[0158] There are many, many types of elastomeric polymers. A briefdescription of the most common classes of elastomers is presented here,with the intent of showing that even with relatively “standard”polymers, many possibilities for bonding exist. Common elastomericpolymers include polyisoprene, polybutadiene, polychloroprene,polyisobutylene, poly(styrene-butadiene-styrene), the polyurethanes, andsilicones.

[0159] Polyisoprene, Polybutadiene, Polychloroprene:

[0160] Polyisoprene, polybutadiene, and polychloroprene are allpolymerized from diene monomers, and therefore have one double bond permonomer when polymerized. This double bond allows the polymers to beconverted to elastomers by vulcanization (essentially, sulfur is used toform crosslinks between the double bonds by heating). This would easilyallow homogeneous multilayer soft lithography by incompletevulcanization of the layers to be bonded; photoresist encapsulationwould be possible by a similar mechanism.

[0161] Polyisobutylene:

[0162] Pure polyisobutylene has no double bonds, but is crosslinked touse as an elastomer by including a small amount (˜1%) of isoprene in thepolymerization. The isoprene monomers give pendant double bonds on thepolyisobutylene backbone, which may then be vulcanized as above.

[0163] Poly(styrene-butadiene-styrene):

[0164] Poly(styrene-butadiene-styrene) is produced by living anionicpolymerization (that is, there is no natural chain-terminating step inthe reaction), so “live” polymer ends can exist in the cured polymer.This makes it a natural candidate for the present photoresistencapsulation system (where there will be plenty of unreacted monomer inthe liquid layer poured on top of the cured layer). Incomplete curingwould allow homogeneous multilayer soft lithography (A to A bonding).The chemistry also facilitates making one layer with extra butadiene(“A”) and coupling agent and the other layer (“B”) with a butadienedeficit (for heterogeneous multilayer soft lithography). SBS is a“thermoset elastomer”, meaning that above a certain temperature it meltsand becomes plastic (as opposed to elastic); reducing the temperatureyields the elastomer again. Thus, layers can be bonded together byheating.

[0165] Polyurethanes:

[0166] Polyurethanes are produced from di-isocyanates (A-A) anddi-alcohols or di-amines (B-B); since there are a large variety ofdi-isocyanates and dialcohols/amines, the number of different types ofpolyurethanes is huge. The A vs. B nature of the polymers, however,would make them usefull for heterogeneous multilayer soft lithographyjust as RTV 615 is: by using excess A-A in one layer and excess B-B inthe other layer.

[0167] Silicones:

[0168] Silicone polymers probably have the greatest structural variety,and almost certainly have the greatest number of commercially availableformulations. The vinyl-to-(Si—H) crosslinking of RTV 615 (which allowsboth heterogeneous multilayer soft lithography and photoresistencapsulation) has already been discussed, but this is only one ofseveral crosslinking methods used in silicone polymer chemistry.

[0169] Cross Linking Agents:

[0170] In addition to the use of the simple “pure” polymers discussedabove, crosslinking agents may be added. Some agents (like the monomersbearing pendant double bonds for vulcanization) are suitable forallowing homogeneous (A to A) multilayer soft lithography or photoresistencapsulation; in such an approach the same agent is incorporated intoboth elastomer layers. Complementary agents (i.e. one monomer bearing apendant double bond, and another bearing a pendant Si—H group) aresuitable for heterogeneous (A to B) multilayer soft lithography. In thisapproach complementary agents are added to adjacent layers.

[0171] Other Materials:

[0172] In addition, polymers incorporating materials such aschlorosilanes or methyl-, ethyl-, and phenylsilanes, andpolydimethylsiloxane (PDMS) such as Dow Chemical Corp. Sylgard 182, 184or 186, or aliphatic urethane diacrylates such as (but not limited to)Ebecryl 270 or Irr 245 from UCB Chemical may also be used.

[0173] The following is a non-exclusive list of elastomeric materialswhich may be utilized in connection with the present invention:polyisoprene, polybutadiene, polychloroprene, polyisobutylene,poly(styrene-butadiene-styrene), the polyurethanes, and siliconepolymers; or poly(bis(fluoroalkoxy)phosphazene) (PNF, Eypel-F),poly(carborane-siloxanes) (Dexsil), poly(acrylonitrile-butadiene)(nitrile rubber), poly(1-butene),poly(chlorotrifluoroethylene-vinylidene fluoride) copolymers (Kel-F),poly(ethyl vinyl ether), poly(vinylidene fluoride), poly(vinylidenefluoride—hexafluoropropylene) copolymer (Viton), elastomericcompositions of polyvinylchloride (PVC), polysulfone, polycarbonate,polymethylmethacrylate (PMMA), and polytertrafluoroethylene (Teflon).

[0174] Doping and Dilution:

[0175] Elastomers may also be “doped” with uncrosslinkable polymerchains of the same class. For instance RTV 615 may be diluted with GESF96-50 Silicone Fluid. This serves to reduce the viscosity of theuncured elastomer and reduces the Young's modulus of the curedelastomer. Essentially, the crosslink-capable polymer chains are spreadfurther apart by the addition of “inert” polymer chains, so this iscalled “dilution”. RTV 615 cures at up to 90% dilution, with a dramaticreduction in Young's modulus.

[0176]FIG. 49 plots Young's modulus versus percentage dilution with GESF96-50 diluent of GE RTV 615 elastomer having a ratio of 30:1 A:B. FIG.49 shows that the flexibility of the elastomer material, and hence theresponsiveness of the valve membrane to an applied actuation force, canbe controlled during fabrication of the device.

[0177] Other examples of doping of elastomer material may include theintroduction of electrically conducting or magnetic species, asdescribed in detail below in conjunction with alternative methods ofactuating the membrane of the device. Should it be desired, doping withfine particles of material having an index of refraction different thanthe elastomeric material (i.e. silica, diamond, sapphire) is alsocontemplated as a system for altering the refractive index of thematerial. Strongly absorbing or opaque particles may be added to renderthe elastomer colored or opaque to incident radiation. This mayconceivably be beneficial in an optically addressable system.

[0178] Finally, by doping the elastomer with specific chemical species,these doped chemical species may be presented at the elastomer surface,thus serving as anchors or starting points for further chemicalderivitization.

[0179] Pre-Treatment and Surface Coating

[0180] Once the elastomeric material has been molded or etched into theappropriate shape, it may be necessary to pre-treat the material inorder to facilitate operation in connection with a particularapplication.

[0181] For example, one possible application for an elastomeric devicein accordance with the present invention is to sort biological entitiessuch as cells or DNA. In such an application, the hydrophobic nature ofthe biological entity may cause it to adhere to the hydrophobicelastomer of the walls of the channel. Therefore, it may be useful topre-treat the elastomeric structure order to impart a hydrophiliccharacter to the channel walls. In an embodiment of the presentinvention utilizing the General Electric RTV 615 elastomer, this can beaccomplished by boiling the shaped elastomer in acid (e.g. 0.01% HCl inwater, pH 2.7, at 60° C. for 40 min).

[0182] Other types of pre-treatment of elastomer material are alsocontemplated by the present application. For example, certain portionsof elastomer may be pre-treated to create anchors for surface chemistryreactions (for example in the formation of peptide chains), or bindingsites for antibodies, as would be advantageous in a given application.Other examples of pre-treatment of elastomer material may include theintroduction of reflective material on the elastomer surface, asdescribed in detail below in conjunction with the micro-mirror arrayapplication.

[0183] Methods of Operating the Present Invention:

[0184]FIGS. 7B and 7H together show the closing of a first flow channelby pressurizing a second flow channel, with FIG. 7B (a front sectionalview cutting through flow channel 32 in corresponding FIG. 7A), showingan open first flow channel 30; with FIG. 7H showing first flow channel30 closed by pressurization of the second flow channel 32.

[0185] Referring to FIG. 7B, first flow channel 30 and second flowchannel 32 are shown. Membrane 25 separates the flow channels, formingthe top of first flow channel 30 and the bottom of second flow channel32. As can be seen, flow channel 30 is “open”.

[0186] As can be seen in FIG. 7H, pressurization of flow channel 32(either by gas or liquid introduced therein) causes membrane 25 todeflect downward, thereby pinching off flow F passing through flowchannel 30. Accordingly, by varying the pressure in channel 32, alinearly actuable valving system is provided such that flow channel 30can be opened or closed by moving membrane 25 as desired. (Forillustration purposes only, channel 30 in FIG. 7G is shown in a “mostlyclosed” position, rather than a “fully closed” position).

[0187] It is to be understood that exactly the same valve opening andclosing methods can be achieved with flow channels 60 and 62.

[0188] Since such valves are actuated by moving the roof of the channelsthemselves (i.e.: moving membrane 25) valves and pumps produced by thistechnique have a truly zero dead volume, and switching valves made bythis technique have a dead volume approximately equal to the activevolume of the valve, for example about 100×100×10 μm=100 pL. Such deadvolumes and areas consumed by the moving membrane are approximately twoorders of magnitude smaller than known conventional microvalves. Smallerand larger valves and switching valves are contemplated in the presentinvention, and a non-exclusive list of ranges of dead volume includes 1aL to 1 uL, 100 aL to 100 nL, 1 fL to 10 nL, 100 fL to 1 nL, and 1 pL to100 pL The extremely small volumes capable of being delivered by pumpsand valves in accordance with the present invention represent asubstantial advantage. Specifically, the smallest known volumes of fluidcapable of being manually metered is around 0.1 μl. The smallest knownvolumes capable of being metered by automated systems is about ten-timeslarger (1 μl). Utilizing pumps and valves in accordance with the presentinvention, volumes of liquid of 10 nl or smaller can routinely bemetered and dispensed. The accurate metering of extremely small volumesof fluid enabled by the present invention would be extremely valuable ina large number of biological applications, including diagnostic testsand assays.

[0189] Equation 1 represents a highly simplified mathematical model ofdeflection of a rectangular, linear, elastic, isotropic plate of uniformthickness by an applied pressure:

w=(BPb ⁴)/(Eh ³),  (1)

[0190] where:

[0191] w=deflection of plate;

[0192] B=shape coefficient (dependent upon length vs. width and supportof edges of plate);

[0193] P=applied pressure;

[0194] b=plate width

[0195] E=Young's modulus; and

[0196] h=plate thickness.

[0197] Thus even in this extremely simplified expression, deflection ofan elastomeric membrane in response to a pressure will be a function of:the length, width, and thickness of the membrane, the flexibility of themembrane (Young's modulus), and the applied actuation force. Becauseeach of these parameters will vary widely depending upon the actualdimensions and physical composition of a particular elastomeric devicein accordance with the present invention, a wide range of membranethicknesses and elasticities, channel widths, and actuation forces arecontemplated by the present invention.

[0198] It should be understood that the formula just presented is onlyan approximation, since in general the membrane does not have uniformthickness, the membrane thickness is not necessarily small compared tothe length and width, and the deflection is not necessarily smallcompared to length, width, or thickness of the membrane. Nevertheless,the equation serves as a useful guide for adjusting variable parametersto achieve a desired response of deflection versus applied force.

[0199]FIGS. 21a and 21 b illustrate valve opening vs. applied pressurefor a 100 μm wide first flow channel 30 and a 50 μm wide second flowchannel 32. The membrane of this device was formed by a layer of GeneralElectric Silicones RTV 615 having a thickness of approximately 30 μm anda Young's modulus of approximately 750 kPa.

[0200]FIGS. 21a and 21 b show the extent of opening of the valve to besubstantially linear over most of the range of applied pressures. Whilethe present invention does not require this linear actuation behavior,embodiments of the invention <insert here>.

[0201] Air pressure was applied to actuate the membrane of the devicethrough a 10 cm long piece of plastic tubing having an outer diameter of0.025″ connected to a 25 mm piece of stainless steel hypodermic tubingwith an outer diameter of 0.025″ and an inner diameter of 0.013″. Thistubing was placed into contact with the control channel by insertioninto the elastomeric block in a direction normal to the control channel.Air pressure was applied to the hypodermic tubing from an external LHDAminiature solenoid valve manufactured by Lee Co.

[0202] Connection of conventional microfluidic devices to an externalfluid flow poses a number of problems avoided by the externalconfiguration just described. One such problem is the fragility of theirconnections with the external environment. Specifically, conventionalmicrofluidic devices are composed of hard, inflexible materials (such assilicon), to which pipes or tubing allowing connection to externalelements must be joined. The rigidity of the conventional materialcreates significant physical stress at points of contact with small anddelicate external tubing, rendering conventional microfluidic devicesprone to fracture and leakage at these contact points.

[0203] By contrast, the elastomer of the present invention is flexibleand can be easily penetrated for external connection by a tube composeda hard material. For example, in an elastomer structure fabricatedutilizing the method shown in FIGS. 1-7B, a hole extending from theexterior surface of the structure into the control channel can be madeby penetrating the elastomer with metal hypodermic tubing after theupper elastomer piece has been removed from the mold (as shown in FIG.3) and before this piece has been bonded to the lower elastomer piece(as shown in FIG. 4). Between these steps, the roof of the controlchannel is exposed to the user's view and is accessible to insertion andproper positioning of the hole. Following completion of fabrication ofthe device, the metal hypodermic tubing is inserted into the hole tocomplete the fluid connection.

[0204] Moreover, the elastomer of the present invention will flex inresponse to physical strain at the point of contact with an externalconnection, rendering the external physical connection more robust. Thisflexibility substantially reduces the chance of leakage or fracture ofthe present device.

[0205] Another disadvantage of conventional microfluidic devices is thedifficulty in establishing an effective seal between the device and itsexternal links. Because of the extremely narrow diameter of the channelsof these devices, even moderate rates of fluid flow can requireextremely high pressures. Unwanted leakage at the junction between thedevice and external connections may result. However, the flexibility ofthe elastomer of the present device also aids in overcoming leakagerelating to pressure. In particular, the flexible elastomeric materialflexes to conform around inserted tubing in order to form a pressureresistant seal.

[0206] While control of the flow of material through the device has sofar been described utilizing applied gas pressure, other fluids could beused. For example, air is compressible, and thus experiences some finitedelay between the time of application of pressure by the externalsolenoid valve and the time that this pressure is experienced by themembrane. In an alternative embodiment of the present invention,pressure could be applied from an external source to a noncompressiblefluid such as water or hydraulic oils, resulting in a near-instantaneoustransfer of applied pressure to the membrane. However, if the displacedvolume of the valve is large or the control channel is narrow, higherviscosity of a control fluid may contribute to delay in actuation. Theoptimal medium for transferring pressure will therefore depend upon theparticular application and device configuration, and both gaseous andliquid media are contemplated by the invention.

[0207] While external applied pressure as described above has beenapplied by a pump/tank system through a pressure regulator and externalminiature valve, other methods of applying external pressure are alsocontemplated in the present invention, including gas tanks, compressors,piston systems, and columns of liquid. Also contemplated is the use ofnaturally occurring pressure sources such as may be found inside livingorganisms, such as blood pressure, gastric pressure, the pressurepresent in the cerebro-spinal fluid, pressure present in theintra-ocular space, and the pressure exerted by muscles during normalflexure. Other methods of regulating external pressure are alsocontemplated, such as miniature valves, pumps, macroscopic peristalticpumps, pinch valves, and other types of fluid regulating equipment suchas is known in the art.

[0208] As can be seen, the response of valves in accordance withembodiments of the present invention have been experimentally shown tobe almost perfectly linear over a large portion of its range of travel,with minimal hysteresis. Accordingly, the present valves are ideallysuited for microfluidic metering and fluid control. The linearity of thevalve response demonstrates that the individual valves are well modeledas Hooke's Law springs. Furthermore, high pressures in the flow channel(i.e.: back pressure) can be countered simply by increasing theactuation pressure. Experimentally, the present inventors have achievedvalve closure at back pressures of 70 kPa, but higher pressures are alsocontemplated. The following is a nonexclusive list of pressure rangesencompassed by the present invention: 10 Pa-25 MPa; 100 Pa-10 Mpa, 1kPa-1 MPa, 1 kPa-300 kPa, 5 kPa-200 kPa, and 15 kPa-100 kPa.

[0209] While valves and pumps do not require linear actuation to openand close, linear response does allow valves to more easily be used asmetering devices. In one embodiment of the invention, the opening of thevalve is used to control flow rate by being partially actuated to aknown degree of closure. Linear valve actuation makes it easier todetermine the amount of actuation force required to close the valve to adesired degree of closure. Another benefit of linear actuation is thatthe force required for valve actuation may be easily determined from thepressure in the flow channel. If actuation is linear, increased pressurein the flow channel may be countered by adding the same pressure (forceper unit area) to the actuated portion of the valve.

[0210] Linearity of a valve depends on the structure, composition, andmethod of actuation of the valve structure. Furthermore, whetherlinearity is a desirable characteristic in a valve depends on theapplication. Therefore, both linearly and nonlinearly actuatable valvesare contemplated in the present invention, and the pressure ranges overwhich a valve is linearly actuatable will vary with the specificembodiment.

[0211]FIG. 22 illustrates time response (i.e.: closure of valve as afunction of time in response to a change in applied pressure) of a 100μm×100 μm×10 μm RTV microvalve with 10-cm-long air tubing connected fromthe chip to a pneumatic valve as described above.

[0212] Two periods of digital control signal, actual air pressure at theend of the tubing and valve opening are shown in FIG. 22. The pressureapplied on the control line is 100 kPa, which is substantially higherthan the ˜40 kPa required to close the valve. Thus, when closing, thevalve is pushed closed with a pressure 60 kPa greater than required.When opening, however, the valve is driven back to its rest positiononly by its own spring force (≦40 kPa). Thus, τ_(close) is expected tobe smaller than τ_(open). There is also a lag between the control signaland control pressure response, due to the limitations of the miniaturevalve used to control the pressure. Calling such lags t and the 1/e timeconstants τ, the values are: t_(open)=3.63 ms, τ_(open)=1.88 ms,t_(close)=2.15 ms, τ_(close)=0.51 ms. If 3τ each are allowed for openingand closing, the valve runs comfortably at 75 Hz when filled withaqueous solution.

[0213] If one used another actuation method which did not suffer fromopening and closing lag, this valve would run at ˜375 Hz. Note also thatthe spring constant can be adjusted by changing the membrane thickness;this allows optimization for either fast opening or fast closing. Thespring constant could also be adjusted by changing the elasticity(Young's modulus) of the membrane, as is possible by introducing dopantinto the membrane or by utilizing a different elastomeric material toserve as the membrane (described above in conjunction with FIGS. 7C-7H.)

[0214] When experimentally measuring the valve properties as illustratedin FIGS. 21 and 22, the valve opening was measured by fluorescence. Inthese experiments, the flow channel was filled with a solution offluorescein isothiocyanate (FITC) in buffer (pH>8) and the fluorescenceof a square area occupying the center ˜⅓rd of the channel is monitoredon an epi-fluorescence microscope with a photomultiplier tube with a 10kHz bandwidth. The pressure was monitored with a Wheatstone-bridgepressure sensor (SenSym SCC15GD2) pressurized simultaneously with thecontrol line through nearly identical pneumatic connections.

[0215] Flow Channel Cross Sections:

[0216] The flow channels of the present invention may optionally bedesigned with different cross sectional sizes and shapes, offeringdifferent advantages, depending upon their desired application. Forexample, the cross sectional shape of the lower flow channel may have acurved upper surface, either along its entire length or in the regiondisposed under an upper cross channel). Such a curved upper surfacefacilitates valve sealing, as follows.

[0217] Referring to FIG. 19, a cross sectional view (similar to that ofFIG. 7B) through flow channels 30 and 32 is shown. As can be seen, flowchannel 30 is rectangular in cross sectional shape. In an alternatepreferred aspect of the invention, as shown in FIG. 20, thecross-section of a flow channel 30 instead has an upper curved surface.

[0218] Referring first to FIG. 19, when flow channel 32 is pressurized,the membrane portion 25 of elastomeric block 24 separating flow channels30 and 32 will move downwardly to the successive positions shown by thedotted lines 25A, 25B, 25C, 25D, and 25E. As can be seen, incompletesealing may possibly result at the edges of flow channel 30 adjacentplanar substrate 14.

[0219] In the alternate preferred embodiment of FIG. 20, flow channel 30a has a curved upper wall 25A. When flow channel 32 is pressurized,membrane portion 25 will move downwardly to the successive positionsshown by dotted lines 25A2, 25A3, 25A4 and 25A5, with edge portions ofthe membrane moving first into the flow channel, followed by topmembrane portions. An advantage of having such a curved upper surface atmembrane 25A is that a more complete seal will be provided when flowchannel 32 is pressurized. Specifically, the upper wall of the flowchannel 30 will provide a continuous contacting edge against planarsubstrate 14, thereby avoiding the “island” of contact seen between wall25 and the bottom of flow channel 30 in FIG. 19.

[0220] Another advantage of having a curved upper flow channel surfaceat membrane 25A is that the membrane can more readily conform to theshape and volume of the flow channel in response to actuation.Specifically, where a rectangular flow channel is employed, the entireperimeter (2× flow channel height, plus the flow channel width) must beforced into the flow channel. However where an arched flow channel isused, a smaller perimeter of material (only the semi-circular archedportion) must be forced into the channel. In this manner, the membranerequires less change in perimeter for actuation and is therefore moreresponsive to an applied actuation force to block the flow channel.

[0221] In an alternate aspect, (not illustrated), the bottom of flowchannel 30 is rounded such that its curved surface mates with the curvedupper wall 25A as seen in FIG. 20 described above.

[0222] In summary, the actual conformational change experienced by themembrane upon actuation will depend upon the configuration of theparticular elastomeric structure. Specifically, the conformationalchange will depend upon the length, width, and thickness profile of themembrane, its attachment to the remainder of the structure, and theheight, width, and shape of the flow and control channels and thematerial properties of the elastomer used. The conformational change mayalso depend upon the method of actuation, as actuation of the membranein response to an applied pressure will vary somewhat from actuation inresponse to a magnetic or electrostatic force.

[0223] Moreover, the desired conformational change in the membrane willalso vary depending upon the particular application for the elastomericstructure. In the simplest embodiments described above, the valve mayeither be open or closed, with metering to control the degree of closureof the valve. In other embodiments however, it may be desirable to alterthe shape of the membrane and/or the flow channel in order to achievemore complex flow regulation. For instance, the flow channel could beprovided with raised protrusions beneath the membrane portion, such thatupon actuation the membrane shuts off only a percentage of the flowthrough the flow channel, with the percentage of flow blockedinsensitive to the applied actuation force.

[0224] Many membrane thickness profiles and flow channel cross-sectionsare contemplated by the present invention, including rectangular,trapezoidal, circular, ellipsoidal, parabolic, hyperbolic, andpolygonal, as well as sections of the above shapes. More complexcross-sectional shapes, such as the embodiment with protrusionsdiscussed immediately above or an embodiment having concavities in theflow channel, are also contemplated by the present invention.

[0225] Alternate Valve Actuation Techniques:

[0226] In addition to pressure based actuation systems described above,optional electrostatic and magnetic actuation systems are alsocontemplated, as follows.

[0227] Electrostatic actuation can be accomplished by forming oppositelycharged electrodes (which will tend to attract one another when avoltage differential is applied to them) directly into the monolithicelastomeric structure. For example, referring to FIG. 7B, an optionalfirst electrode 70 (shown in phantom) can be positioned on (or in)membrane 25 and an optional second electrode 72 (also shown in phantom)can be positioned on (or in) planar substrate 14. When electrodes 70 and72 are charged with opposite polarities, an attractive force between thetwo electrodes will cause membrane 25 to deflect downwardly, therebyclosing the “valve” (i.e.: closing flow channel 30).

[0228] For the membrane electrode to be sufficiently conductive tosupport electrostatic actuation, but not so mechanically stiff so as toimpede the valve's motion, a sufficiently flexible electrode must beprovided in or over membrane 25. Such an electrode may be provided by athin metallization layer, doping the polymer with conductive material,or making the surface layer out of a conductive material.

[0229] In an exemplary aspect, the electrode present at the deflectingmembrane can be provided by a thin metallization layer which can beprovided, for example, by sputtering a thin layer of metal such as 20 nmof gold. In addition to the formation of a metallized membrane bysputtering, other metallization approaches such as chemical epitaxy,evaporation, electroplating, and electroless plating are also available.Physical transfer of a metal layer to the surface of the elastomer isalso available, for example by evaporating a metal onto a flat substrateto which it adheres poorly, and then placing the elastomer onto themetal and peeling the metal off of the substrate.

[0230] A conductive electrode 70 may also be formed by depositing carbonblack (i.e. Cabot Vulcan XC72R) on the elastomer surface, either bywiping on the dry powder or by exposing the elastomer to a suspension ofcarbon black in a solvent which causes swelling of the elastomer, (suchas a chlorinated solvent in the case of PDMS). Alternatively, theelectrode 70 may be formed by constructing the entire layer 20 out ofelastomer doped with conductive material (i.e. carbon black or finelydivided metal particles). Yet further alternatively, the electrode maybe formed by electrostatic deposition, or by a chemical reaction thatproduces carbon. In experiments conducted by the present inventors,conductivity was shown to increase with carbon black concentration from5.6×10⁻¹⁶ to about 5×10⁻³ (Ω-cm)⁻¹. The lower electrode 72, which is notrequired to move, may be either a compliant electrode as describedabove, or a conventional electrode such as evaporated gold, a metalplate, or a doped semiconductor electrode.

[0231] Alternatively, magnetic actuation of the flow channels can beachieved by fabricating the membrane separating the flow channels with amagnetically polarizable material such as iron, or a permanentlymagnetized material such as polarized NdFeB. In experiments conducted bythe present inventors, magnetic silicone was created by the addition ofiron powder (about 1 um particle size), up to 20% iron by weight.

[0232] Where the membrane is fabricated with a magnetically polarizablematerial, the membrane can be actuated by attraction in response to anapplied magnetic field Where the membrane is fabricated with a materialcapable of maintaining permanent magnetization, the material can firstbe magnetized by exposure to a sufficiently high magnetic field, andthen actuated either by attraction or repulsion in response to thepolarity of an applied inhomogenous magnetic field.

[0233] The magnetic field causing actuation of the membrane can begenerated in a variety of ways. In one embodiment, the magnetic field isgenerated by an extremely small inductive coil formed in or proximate tothe elastomer membrane. The actuation effect of such a magnetic coilwould be localized, allowing actuation of individual pump and/or valvestructures. Alternatively, the magnetic field could be generated by alarger, more powerfiul source, in which case actuation would be globaland would actuate multiple pump and/or valve structures at one time.

[0234] It is further possible to combine pressure actuation withelectrostatic or magnetic actuation. Specifically, a bellows structurein fluid communication with a recess could be electrostatically ormagnetically actuated to change the pressure in the recess and therebyactuate a membrane structure adjacent to the recess.

[0235] In addition to electrical or magnetic actuation as describedabove, optional electrolytic and electrokinetic actuation systems arealso contemplated by the present invention. For example, actuationpressure on the membrane could arise from an electrolytic reaction in arecess overlying the membrane. In such an embodiment, electrodes presentin the recess would apply a voltage across an electrolyte in the recess.This potential difference would cause electrochemical reaction at theelectrodes and result in the generation of gas species, giving rise to apressure differential in the recess.

[0236] Alternatively, actuation pressure on the membrane could arisefrom an electrokinetic fluid flow in the control channel. In such anembodiment, electrodes present at opposite ends of the control channelwould apply a potential difference across an electrolyte present in thecontrol channel. Migration of charged species in the electrolyte to therespective electrodes could give rise to a pressure differential.

[0237] Finally, it is also possible to actuate the device by causing afluid flow in the control channel based upon the application of thermalenergy, either by thermal expansion or by production of gas from liquid.Similarly, chemical reactions generating gaseous products may produce anincrease in pressure sufficient for membrane actuation.

[0238] Networked Systems:

[0239]FIGS. 23A and 23B show a views of a single on/off valve, identicalto the systems set forth above, (for example in FIG. 7A). FIGS. 24A and24B shows a peristaltic pumping system comprised of a plurality of thesingle addressable on/off valves as seen in FIG. 23, but networkedtogether. FIG. 25 is a graph showing experimentally achieved pumpingrates vs. frequency for the peristaltic pumping system of FIG. 24. FIGS.26A and 26B show a schematic view of a plurality of flow channels whichare controllable by a single control line. This system is also comprisedof a plurality of the single addressable on/off valves of FIG. 23,multiplexed together, but in a different arrangement than that of FIG.23. FIG. 27 is a schematic illustration of a multiplexing system adaptedto permit fluid flow through selected channels, comprised of a pluralityof the single on/off valves of FIG. 23, joined or networked together.

[0240] Referring first to FIGS. 23A and 23B, a schematic of flowchannels 30 and 32 is shown. Flow channel 30 preferably has a fluid (orgas) flow F passing therethrough. Flow channel 32, (which crosses overflow channel 30, as was already explained herein), is pressurized suchthat membrane 25 separating the flow channels may be depressed into thepath of flow channel 30, shutting off the passage of flow Ftherethrough, as has been explained. As such, “flow channel” 32 can alsobe referred to as a “control line” which actuates a single valve in flowchannel 30. In FIGS. 23 to 26, a plurality of such addressable valvesare joined or networked together in various arrangements to producepumps, capable of peristaltic pumping, and other fluidic logicapplications.

[0241] Referring to FIG. 24A and 24B, a system for peristaltic pumpingis provided, as follows. A flow channel 30 has a plurality of generallyparallel flow channels (i.e.: control lines) 32A, 32B and 32C passingthereover. By pressurizing control line 32A, flow F through flow channel30 is shut off under membrane 25A at the intersection of control line32A and flow channel 30. Similarly, (but not shown), by pressurizingcontrol line 32B, flow F through flow channel 30 is shut off undermembrane 25B at the intersection of control line 32B and flow channel30, etc.

[0242] Each of control lines 32A, 32B, and 32C is separatelyaddressable. Therefore, peristalsis may be actuated by the pattern ofactuating 32A and 32C together, followed by 32A, followed by 32A and 32Btogether, followed by 32B, followed by 32B and C together, etc. Thiscorresponds to a successive “101, 100, 110, 010, 011, 001” pattern,where “0” indicates “valve open” and “1” indicates “valve closed.” Thisperistaltic pattern is also known as a 120° pattern (referring to thephase angle of actuation between three valves). Other peristalticpatterns are equally possible, including 60° and 90° patterns.

[0243] In experiments performed by the inventors, a pumping rate of 2.35nL/s was measured by measuring the distance traveled by a column ofwater in thin (0.5 mm i.d.) tubing; with 100×100×10 μm valves under anactuation pressure of 40 kPa. The pumping rate increased with actuationfrequency until approximately 75 Hz, and then was nearly constant untilabove 200 Hz. The valves and pumps are also quite durable and theelastomer membrane, control channels, or bond have never been observedto fail. In experiments performed by the inventors, none of the valvesin the peristaltic pump described herein show any sign of wear orfatigue after more than 4 million actuations. In addition to theirdurability, they are also gentle. A solution of E. Coli pumped through achannel and tested for viability showed a 94% survival rate.

[0244]FIG. 25 is a graph showing experimentally achieved pumping ratesvs. frequency for the peristaltic pumping system of FIG. 24.

[0245]FIGS. 26A and 26B illustrates another way of assembling aplurality of the addressable valves of FIG. 21. Specifically, aplurality of parallel flow channels 30A, 30B, and 30C are provided. Flowchannel (i.e.: control line) 32 passes thereover across flow channels30A, 30B, and 30C. Pressurization of control line 32 simultaneouslyshuts off flows F1, F2 and F3 by depressing membranes 25A, 25B, and 25Clocated at the intersections of control line 32 and flow channels 30A,30B, and 30C.

[0246]FIG. 27 is a schematic illustration of a multiplexing systemadapted to selectively permit fluid to flow through selected channels,as follows. The downward deflection of membranes separating therespective flow channels from a control line passing thereabove (forexample, membranes 25A, 25B, and 25C in FIGS. 26A and 26B) dependsstrongly upon the membrane dimensions. Accordingly, by varying thewidths of flow channel control line 32 in FIGS. 26A and 26B, it ispossible to have a control line pass over multiple flow channels, yetonly actuate (i.e.: seal) desired flow channels. FIG. 27 illustrates aschematic of such a system, as follows.

[0247] A plurality of parallel flow channels 30A, 30B, 30C, 30D, 30E and30F are positioned under a plurality of parallel control lines 32A, 32B,32C, 32D, 32E and 32F. Control channels 32A, 32B, 32C, 32D, 32E and 32Fare adapted to shut off fluid flows F1, F2, F3, F4, F5 and F6 passingthrough parallel flow channels 30A, 30B, 30C, 30D, 30E and 30F using anyof the valving systems described above, with the following modification.

[0248] Each of control lines 32A, 32B, 32C, 32D, 32E and 32F have bothwide and narrow portions. For example, control line 32A is wide inlocations disposed over flow channels 30A, 30C and 30E. Similarly,control line 32B is wide in locations disposed over flow channels 30B,30D and 30F, and control line 32C is wide in locations disposed overflow channels 30A, 30B, 30E and 30F.

[0249] At the locations where the respective control line is wide, itspressurization will cause the membrane (25) separating the flow channeland the control line to depress significantly into the flow channel,thereby blocking the flow passage therethrough. Conversely, in thelocations where the respective control line is narrow, membrane (25)will also be narrow. Accordingly, the same degree of pressurization willnot result in membrane (25) becoming depressed into the flow channel(30). Therefore, fluid passage thereunder will not be blocked.

[0250] For example, when control line 32A is pressurized, it will blockflows F1, F3 and F5 in flow channels 30A, 30C and 30E. Similarly, whencontrol line 32C is pressurized, it will block flows F1, F2, F5 and F6in flow channels 30A, 30B, 30E and 30F. As can be appreciated, more thanone control line can be actuated at the same time. For example, controllines 32A and 32C can be pressurized simultaneously to block all fluidflow except F4 (with 32A blocking F1, F3 and F5; and 32C blocking F1,F2, F5 and F6).

[0251] By selectively pressurizing different control lines (32) bothtogether and in various sequences, a great degree of fluid flow controlcan be achieved. Moreover, by extending the present system to more thansix parallel flow channels (30) and more than four parallel controllines (32), and by varying the positioning of the wide and narrow 10regions of the control lines, very complex fluid flow control systemsmay be fabricated. A property of such systems is that it is possible toturn on any one flow channel out of n flow channels with only 2(log₂n)control lines.

[0252] The inventors have succeeded in fabricating microfluidicstructures with densities of 30 devices/but greater densities areachievable.

[0253] Selectively Addressable Reaction Chambers Along Flow Lines:

[0254] In a further embodiment of the invention, illustrated in FIGS.28A, 28B, 28C and 28D, a system for selectively directing fluid flowinto one more of a plurality of reaction chambers disposed along a flowline is provided.

[0255]FIG. 28A shows a top view of a flow channel 30 having a pluralityof reaction chambers 80A and 80B disposed therealong. Preferably flowchannel 30 and reaction chambers 80A and 80B are formed together asrecesses into the bottom surface of a first layer 100 of elastomer.

[0256]FIG. 28B shows a bottom plan view of another elastomeric layer 110with two control lines 32A and 32B each being generally narrow, buthaving wide extending portions 33A and 33B formed as recesses therein.

[0257] As seen in the exploded view of FIG. 28C, and assembled view ofFIG. 28D, elastomeric layer 110 is placed over elastomeric layer 100.Layers 100 and 110 are then bonded together, and the integrated systemoperates to selectively direct fluid flow F (through flow channel 30)into either or both of reaction chambers 80A and 80B, as follows.Pressurization of control line 32A will cause the membrane 25 (i.e.: thethin portion of elastomer layer 100 located below extending portion 33Aand over regions 82A of reaction chamber 80A) to become depressed,thereby shutting off fluid flow passage in regions 82A, effectivelysealing reaction chamber 80 from flow channel 30. As can also be seen,extending portion 33A is wider than the remainder of control line 32A.

[0258] As such, pressurization of control line 32A will not result incontrol line 32A sealing flow channel 30.

[0259] As can be appreciated, either or both of control lines 32A and32B can be actuated at once. When both control lines 32A and 32B arepressurized together, sample flow in flow channel 30 will enter neitherof reaction chambers 80A or 80B.

[0260] The concept of selectably controlling fluid introduction intovarious addressable reaction chambers disposed along a flow line (FIGS.28) can be combined with concept of selectably controlling fluid flowthrough one or more of a plurality of parallel flow lines (FIG. 27) toyield a system in which a fluid sample or samples can be can be sent toany particular reaction chamber in an array of reaction chambers. Anexample of such a system is provided in FIG. 29, in which parallelcontrol channels 32A, 32B and 32C with extending portions 34 (all shownin phantom) selectively direct fluid flows F1 and F2 into any of thearray of reaction wells 80A, 80B, 80C or 80D as explained above; whilepressurization of control lines 32C and 32D selectively shuts off flowsF2 and Fl, respectively.

[0261] In yet another novel embodiment, fluid passage between parallelflow channels is possible. Referring to FIG. 30, either or both ofcontrol lines 32A or 32D can be depressurized such that fluid flowthrough lateral passageways 35 (between parallel flow channels 30A and30B) is permitted. In this aspect of the invention, pressurization ofcontrol lines 32C and 32D would shut flow channel 30A between 35A and35B, and would also shut lateral passageways 35B. As such, flow enteringas flow F1 would sequentially travel through 30A, 35A and leave 30B asflow F4.

[0262] Switchable Flow Arrays

[0263] In yet another novel embodiment, fluid passage can be selectivelydirected to flow in either of two perpendicular directions. An exampleof such a “switchable flow array” system is provided in FIGS. 31A to31D. FIG. 31A shows a bottom view of a first layer of elastomer 90, (orany other suitable substrate), having a bottom surface with a pattern ofrecesses forming a flow channel grid defined by an array of solid posts92, each having flow channels passing therearound.

[0264] In preferred aspects, an additional layer of elastomer is boundto the top surface of layer 90 such that fluid flow can be selectivelydirected to move either in direction F1, or perpendicular direction F2.. FIG. 31 is a bottom view of the bottom surface of the second layer ofelastomer 95 showing recesses formed in the shape of alternating“vertical” control lines 96 and “horizontal” control lines 94.“Vertical” control lines 96 have the same width therealong, whereas“horizontal” control lines 94 have alternating wide and narrow portions,as shown.

[0265] Elastomeric layer 95 is positioned over top of elastomeric layer90 such that “vertical” control lines 96 are positioned over posts 92 asshown in FIG. 31 C and “horizontal” control lines 94 are positioned withtheir wide portions between posts 92, as shown in FIG. 31D.

[0266] As can be seen in FIG. 31C, when “vertical” control lines 96 arepressurized, the membrane of the integrated structure formed by theelastomeric layer initially positioned between layers 90 and 95 inregions 98 will be deflected downwardly over the array of flow channelssuch that flow in only able to pass in flow direction F2 (i.e.:vertically), as shown.

[0267] As can be seen in FIG. 31D, when “horizontal” control lines 94are pressurized, the membrane of the integrated structure formed by theelastomeric layer initially positioned between layers 90 and 95 inregions 99 will be deflected downwardly over the array of flow channels,(but only in the regions where they are widest), such that flow in onlyable to pass in flow direction F1 (i.e.: horizontally), as shown.

[0268] The design illustrated in FIGS. 31 allows a switchable flow arrayto be constructed from only two elastomeric layers, with no verticalvias passing between control lines in different elastomeric layersrequired. If all vertical flow control lines 94 are connected, they maybe pressurized from one input. The same is true for all horizontal flowcontrol lines 96.

[0269] Biopolymer Synthesis

[0270] The present elastomeric valving structures can also be used inbiopolymer synthesis, for example, in synthesizing oligonucleotides,proteins, peptides, DNA, etc. In a preferred aspect, such biopolymersynthesis systems may comprise an integrated system comprising an arrayof reservoirs, fluidic logic (according to the present invention) forselecting flow from a particular reservoir, an array of channels orreservoirs in which synthesis is performed, and fluidic logic (alsoaccording to the present invention) for determining into which channelsthe selected reagent flows. An example of such a system 200 isillustrated in FIG. 32, as follows.

[0271] Four reservoirs 150A, 150B, 150C and 150D have bases A, C, T andG respectively disposed therein, as shown. Four flow channels 30A, 30B,30C and 30D are connected to reservoirs 150A, 150B, 150C and 150D. Fourcontrol lines 32A, 32B, 32C and 32D (shown in phantom) are disposedthereacross with control line 32A permitting flow only through flowchannel 30A (i.e.: sealing flow channels 30B, 30C and 30D), when controlline 32A is pressurized. Similarly, control line 32B perrnits flow onlythrough flow channel 30B when pressurized. As such, the selectivepressurization of control lines 32A, 32B, 32C and 32D sequentiallyselects a desired base A, C, T and G from a desired reservoir 150A,150B, 150C or 150D. The fluid then passes through flow channel 120 intoa multiplexed channel flow controller 125, (including, for example, anysystem as shown in FIGS. 26A to 31D) which in turn directs fluid flowinto one or more of a plurality of synthesis channels or chambers 122A,122B, 122C, 122D or 122E in which solid phase synthesis may be carriedout.

[0272]FIG. 33 shows a further extension of this system on which aplurality of reservoirs R1 to R13 (which may contain bases A, T, C andG, or any other reactants, such as would be used in combinatorialchemistry), are connected to systems 200 as set forth in FIGS. 32.Systems 200 are connected to a multiplexed channel flow controller 125,(including, for example, any system as shown in FIGS. 26A to 31D) whichis in turn connected to a switchable flow array (for example as shown inFIGS. 31). An advantage of this system is that both of multiplexedchannel flow controllers 125 and fluid selection systems 200 can becontrolled by the same pressure inputs 170 and 172, provided a “closehorizontal” and a “close vertical” control lines (160 and 162, inphantom) are also provided.

[0273] In further alternate aspects of the invention, a plurality ofmultiplexed channel flow controllers (such as 125) may be used, witheach flow controller initially positioned stacked above one another on adifferent elastomeric layer, with vertical vias or interconnects betweenthe elastomer layers (which may be created by lithographicallypatterning an etch resistant layer on top of a elastomer layer, thenetching the elastomer and finally removing the etch resist before addingthe last layer of elastomer).

[0274] For example, a vertical via in an elastomer layer can be createdby etching a hole down onto a raised line on a micromachined mold, andbonding the next layer such that a channel passes over that hole. Inthis aspect of the invention, multiple synthesis with a plurality ofmultiplexed channel flow controllers 125 is possible.

[0275] The bonding of successive layers of molded elastomer to form amultilayer structure is shown in FIG. 34, which is an optical micrographof a section of a test structure composed of seven layers of elastomer.The scale bar of FIG. 34 is 200 μm.

[0276] One method for fabricating an elastomer layer having the verticalvia feature utilized in a multi-layer structure is shown in FIGS.35A-35D. FIG. 35A shows formation of elastomer layer 3500 overmicromachined mold 3502 including raised line 3502 a.

[0277]FIG. 35B shows formation of metal etch blocking layer 3504 overelastomer layer 3500, followed by the patterning of photoresist mask3506 over etch blocking layer 3504 to cover masked regions 3508 andleave exposed unmasked regions 3510. FIG. 35C shows the exposure tosolvent which removes etch blocking layer 3504 in unmasked regions 3510.

[0278]FIG. 35D shows removal of the patterned photoresist, followed bysubsequent etching of underlying elastomer 3500 in unmasked regions 3510to form vertical via 3512. Subsequent exposure to solvent removesremaining etch blocking layer 3504 in masked regions 3508 selective tothe surrounding elastomer 3500 and mold 3502. This elastomer layer maythen be incorporated into an elastomer structure by multilayer softlithography.

[0279] This series of steps can be repeated as necessary to form amulti-layered structure having the desired number and orientation ofvertical vias between channels of successive elastomer layers.

[0280] The inventors of the present invention have succeeded in etchingvias through GE RTV 615 layers using a solution of Tetrabutylammoniumfluoride in organic solvent. Gold serves as the etch blocking material,with gold removed selective to GE RTV 615 utilizing a KI/I₂/H₂O mixture.

[0281] Alternatively, vertical vias between channels in successiveelastomer layers could be formed utilizing a negative mask technique. Inthis approach, a negative mask of a metal foil is patterned, andsubsequent formation of an etch blocking layer is inhibited where themetal foil is present. Once the etch blocking material is patterned, thenegative metal foil mask is removed, permitting selective etching of theelastomer as described above.

[0282] In yet another approach, vertical vias could be formed in anelastomer layer using ablation of elastomer material through applicationof radiation from an applied laser beam.

[0283] While the above approach is described in connection with thesynthesis of biopolymers, the invention is not limited to thisapplication. The present invention could also function in a wide varietyof combinatorial chemical synthesis approaches.

[0284] Other Applications:

[0285] Advantageous applications of the present monolithicmicrofabricated elastomeric valves and pumps are numerous. Accordingly,the present invention is not limited to any particular application oruse thereof. In preferred aspects, the following uses and applicationsfor the present invention are contemplated.

[0286] 1. Cell/DNA Sorting

[0287] The present microfluidic pumps and valves can also be used inflow cytometers for cell sorting and DNA sizing. Sorting of objectsbased upon size is extremely useful in many technical fields.

[0288] For example, many assays in biology require determination of thesize of molecular-sized entities. Of particular importance is themeasurement of length distribution of DNA molecules in a heterogeneoussolution. This is commonly done using gel electrophoresis, in which themolecules are separated by their differing mobility in a gel matrix inan applied electric field, and their positions detected by absorption oremission of radiation. The lengths of the DNA molecules are theninferred from their mobility.

[0289] While powerful, electrophoretic methods pose disadvantages. Formedium to large DNA molecules, resolution, i.e. the minimum lengthdifference at which different molecular lengths may be distinguished, islimited to approximately 10% of the total length. For extremely largeDNA molecules, the conventional sorting procedure is not workable.Moreover, gel electrophoresis is a relatively lengthy procedure, and mayrequire on the order of hours or days to perform.

[0290] The sorting of cellular-sized entities is also an important task.Conventional flow cell sorters are designed to have a flow chamber witha nozzle and are based on the principle of hydrodynamic focusing withsheath flow. Most conventional cell sorters combine the technology ofpiezo-electric drop generation and electrostatic deflection to achievedroplet generation and high sorting rates. However, this approach offerssome important disadvantages. One disadvantage is that the complexity,size, and expense of the sorting device requires that it be reusable inorder to be cost-effective. Reuse can in turn lead to problems withresidual materials causing contamination of samples and turbulent fluidflow.

[0291] Therefore, there is a need in the art for a simple, inexpensive,and easily fabricated sorting device which relies upon the mechanicalcontrol of fluid flow rather than upon electrical interactions betweenthe particle and the solute.

[0292]FIG. 36 shows one embodiment of a sorting device in accordancewith the present invention. Sorting device 3600 is formed from aswitching valve structure created from channels present in anelastomeric block. Specifically, flow channel 3602 is T-shaped, withstem 3602 a of flow channel 3602 in fluid communication with samplereservoir 3604 containing sortable entities 3606 of different typesdenoted by shape (square, circle, triangle, etc.). Left branch 3602 b offlow channel 3602 is in fluid communication with waste reservoir 3608.Right branch 3602 c of flow channel 3602 is in communication withcollection reservoir 3610.

[0293] Control channels 3612 a, 3612 b, and 3612 c overlie and areseparated from stem 3602 a of flow channel 3602 by elastomeric membraneportions 3614 a, 3614 b, and 3614 c respectively. Together, stem 3602 aof flow channel 3602 and control channels 3612 a, 3612 b, and 3612 cform first peristaltic pump structure 3616 similar to that described atlength above in connection with FIG. 24a.

[0294] Control channel 3612 d overlies and is separated from rightbranch 3602 c of flow channel 3602 by elastomeric membrane portion 3614d. Together, right branch 3602 c of flow channel 3602 and controlchannels 3612 d forms first valve structure 3618 a. Control channel 3612e overlies and is separated from left branch 3602 c of flow channel 3602by elastomeric membrane portion 3614 e. Together, left branch 3602 c offlow channel 3602 and control channel 3612 e forms second valvestructure 3618 b.

[0295] As shown in FIG. 36, stem 3602 a of flow channel 3602 narrowsconsiderably as it approaches detection widow 3620 adjacent to thejunction of stem 3602 a, right branch 3602 b, and left branch 3602 c.Detection window 3620 is of sufficient width to allow for uniformillumination of this region. In one embodiment, the width of the stemnarrows from 100 μm to 5 μm at the detection window. The width of thestem at the detection window can be precisely formed using the softlithography or photoresist encapsulation fabrication techniquesdescribed extensively above, and will be depend upon the nature and sizeof the entity to be sorted.

[0296] Operation of sorting device in accordance with one embodiment ofthe present invention is as follows.

[0297] The sample is diluted to a level such that only a single sortableentity would be expected to be present in the detection window at anytime. Peristaltic pump 3616 is activated by flowing a fluid throughcontrol channels 3612 a-c as described extensively above. In addition,second valve structure 3618 b is closed by flowing fluid through controlchannel 3612 e. As a result of the pumping action of peristaltic pump3616 and the blocking action of second valve 3618 b, fluid flows fromsample reservoir 3604 through detection window 3620 into waste reservoir3608. Because of the narrowing of stem 3604, sortable entities presentin sample reservoir 3604 are carried by this regular fluid flow, one ata time, through detection window 3620.

[0298] Radiation 3640 from source 3642 is introduced into detectionwindow 3620. This is possible due to the transmissive property of theelastomeric material. Absorption or emission of radiation 3640 bysortable entity 3606 is then detected by detector 3644.

[0299] If sortable entity 3606 a within detection window 3620 isintended to be segregated and collected by sorting device 3600, firstvalve 3618 a is activated and second valve 3618 b is deactivated. Thishas the effect of drawing sortable entity 3606 a into collectionreservoir 3610, and at the same time transferring second sortable entity3606 b into detection window 3620. If second sortable entity 3602 b isalso identified for collection, peristaltic pump 3616 continues to flowfluid through right branch 3602 c of flow channel 3602 into collectionreservoir 3610. However, if second entity 3606 b is not to be collected,first valve 3618 a opens and second valve 3618 b closes, and firstperistaltic pump 3616 resumes pumping liquid through left branch 3602 bof flow channel 3602 into waste reservoir 3608.

[0300] While one specific embodiment of a sorting device and a methodfor operation thereof is described in connection with FIG. 36, thepresent invention is not limited to this embodiment. For example, fluidneed not be flowed through the flow channels using the peristaltic pumpstructure, but could instead be flowed under pressure with theelastomeric valves merely controlling the directionality of flow. In yetanother embodiment, a plurality of sorting structures could be assembledin series in order to perform successive sorting operations, with thewaste reservoir of FIG. 36 simply replaced by the stem of the nextsorting structure.

[0301] Moreover, a high throughput method of sorting could be employed,wherein a continuous flow of fluid from the sample reservoir through thewindow and junction into the waste reservoir is maintained until anentity intended for collection is detected in the window. Upon detectionof an entity to be collected, the direction of fluid flow by the pumpstructure is temporarily reversed in order to transport the desiredparticle back through the junction into the collection reservoir. Inthis manner, the sorting device could utilize a higher flow rate, withthe ability to backtrack when a desired entity is detected. Such analternative high throughput sorting technique could be used when theentity to be collected is rare, and the need to backtrack infrequent.

[0302] Sorting in accordance with the present invention would avoid thedisadvantages of sorting utilizing conventional electrokinetic flow,such as bubble formation, a strong dependence of flow magnitude anddirection on the composition of the solution and surface chemistryeffects, a differential mobility of different chemical species, anddecreased viability of living organisms in the mobile medium.

[0303] 2. Semiconductor Processing

[0304] Systems for semiconductor gas flow control, (particularly forepitaxial applications in which small quantities of gases are accuratelymetered), are also contemplated by the present invention. For example,during fabrication of semiconductor devices solid material is depositedon top of a semiconductor substrate utilizing chemical vapor deposition(CVD). This is accomplished by exposing the substrate to a mixture ofgas precursor materials, such that these gases react and the resultingproduct crystallizes on top of the substrate.

[0305] During such CVD processes, conditions must be carefullycontrolled to ensure uniform deposition of material free of defects thatcould degrade the operation of the electrical device. One possiblesource of nonuniformity is variation in the flow rate of reactant gasesto the region over the substrate. Poor control of the gas flow rate canalso lead to variations in the layer thicknesses from run to run, whichis another source of error. Unfortunately, there has been a significantproblem in controlling the amount of gas flowed into the processingchamber, and maintaining stable flow rates in conventional gas deliverysystems.

[0306] Accordingly, FIG. 37A shows one embodiment of the presentinvention adapted to convey, at precisely-controllable flow rates,processing gas over the surface of a semiconductor wafer during a CVDprocess. Specifically, semiconductor wafer 3700 is positioned upon wafersupport 3702 located within a CVD chamber. Elastomeric structure 3704containing a large number of evenly distributed orifices 3706 ispositioned just above the surface of wafer 3700.

[0307] A variety of process gases are flowed at carefully controlledrates from reservoirs 3708 a and 3708 b, through flow channels inelastomeric block 3704, and out of orifices 3706. As a result of theprecisely controlled flow of process gases above wafer 3700, solidmaterial 3710 having an extremely uniform structure is deposited.

[0308] Precise metering of reactant gas flow rates utilizing valveand/or pump structures of the present invention is possible for severalreasons. First, gases can be flowed through valves that respond in alinear fashion to an applied actuation pressure, as is discussed abovein connection with FIGS. 21A and 21B. Alternatively or in addition tometering of gas flow using valves, the predictable behavior of pumpstructures in accordance with the present invention can be used toprecisely meter process gas flow.

[0309] In addition to the chemical vapor deposition processes describedabove, the present technique is also useful to control gas flow intechniques such as molecular -beam epitaxy and reactive ion etching.

[0310] 3. Micro Mirror Arrays

[0311] While the embodiments of the present invention described thus farrelate to operation of a structure composed entirely of elastomericmaterial, the present invention is not limited to this type ofstructure. Specifically, it is within the scope of the present inventionto combine an elastomeric structure with a conventional, silicon-basedsemiconductor structure.

[0312] For example, further contemplated uses of the presentmicrofabricated pumps and valves are in optical displays in which themembrane in an elastomeric structure reflects light either as a flatplanar or as a curved surface depending upon whether the membrane isactivated. As such, the membrane acts as a switchable pixel. An array ofsuch switchable pixels, with appropriate control circuitry, could beemployed as a digital or analog micro mirror array.

[0313] Accordingly, FIG. 38 shows an exploded view of a portion of oneembodiment of a micro mirror array in accordance with the presentinvention.

[0314] Micro mirror array 3800 includes first elastomer layer 3802overlying and separated from and underlying semiconductor structure 3804by second elastomer layer 3806. Surface 3804 a of semiconductorstructure 3804 bears a plurality of electrodes 3810. Electrodes 3810 areindividually addressable through conducting row and column lines, aswould be known to one of ordinary skill in the art.

[0315] First elastomeric layer 3802 includes a plurality of intersectingchannels 3822 underlying an electrically conducting, reflectingelastomeric membrane portion 3802 a. First elastomeric layer 3802 isaligned over second elastomeric layer 3806 and underlying semiconductordevice 3804 such that points of intersection of channels 3822 overlieelectrodes 3810.

[0316] In one embodiment of a method of fabrication in accordance withthe present invention, first elastomeric layer 3822 may be formed byspincoating elastomeric material onto a mold featuring intersectingchannels, curing the elastomer, removing the shaped elastomer from themold, and introducing electrically conducting dopant into surface regionof the shaped elastomer. Alternatively as described in connection withFIGS. 7C-7G above, first elastomeric layer 3822 may be formed from twolayers of elastomer by inserting elastomeric material into a moldcontaining intersecting channels such that the elastomeric material isflush with the height of the channel walls, and then bonding a separatedoped elastomer layer to the existing elastomeric material to form amembrane on the top surface.

[0317] Alternatively, the first elastomeric layer 3802 may be producedfrom electrically conductive elastomer, where the electricalconductivity is due either to doping or to the intrinsic properties ofthe elastomer material.

[0318] During operation of reflecting structure 3800, electrical signalsare communicated along a selected row line and column line to electrode3810 a. Application of voltage to electrode 3810 a generates anattractive force between electrode 3810 a and overlying membrane 3802 a.This attractive force actuates a portion of membrane 3802 a, causingthis membrane portion to flex downward into the cavity resulting fromintersection of the channels 3822. As a result of distortion of membrane3802 a from planar to concave, light is reflected differently at thispoint in the surface of elastomer structure 3802 than from thesurrounding planar membrane surface. A pixel image is thereby created.

[0319] The appearance of this pixel image is variable, and may becontrolled by altering the magnitude of voltage applied to theelectrode. A higher voltage applied to the electrode will increase theattractive force on the membrane portion, causing further distortion inits shape. A lower voltage applied to the electrode will decrease theattractive force on the membrane, reducing distortion in its shape fromthe planar. Either of these changes will affect the appearance of theresulting pixel image.

[0320] A variable micro mirror array structure as described could beused in a variety of applications, including the display of images.Another application for a variable micro mirror array structure inaccordance with an embodiment of the present invention would be as ahigh capacity switch for a fiber optics communications system, with eachpixel capable of affecting the reflection and transfer of a component ofan incident light signal.

[0321] 5. Refracting Structures

[0322] The micro-mirror array structure just described controlsreflection of incident light. However, the present invention is notlimited to controlling reflection. Yet another embodiment of the presentinvention enables the exercise of precise control over refraction ofincident light in order to create lens and filter structures.

[0323]FIG. 39 shows one embodiment of a refractive structure inaccordance with the present invention. Refractive structure 3900includes first elastomeric layer 3902 and second elastomeric layer 3904composed of elastomeric material capable of transmitting incident light3906.

[0324] First elastomeric layer 3902 has convex portion 3902 a which maybe created by curing elastomeric material formed over a micromachinedmold having a concave portion. Second elastomeric layer 3904 has a flowchannel 3905 and may be created from a micromachined mold having araised line as discussed extensively above.

[0325] First elastomer layer 3902 is bonded to second elastomer layer3904 such that convex portion 3902 a is positioned above flow channel3905. This structure can serve a variety of purposes.

[0326] For example, light incident to elastomeric structure 3900 wouldbe focused into the underlying flow channel, allowing the possibleconduction of light through the flow channel. Alternatively, in oneembodiment of an elastomeric device in accordance with the presentinvention, fluorescent or phosphorescent liquid could be flowed throughthe flow channel, with the resulting light from the fluid refracted bythe curved surface to form a display.

[0327]FIG. 40 shows another embodiment of a refractive structure inaccordance with the present invention. Refractive structure 4000 is amultilayer optical train based upon a Fresnel lens design. Specifically,refractive structure 4000 is composed of four successive elastomerlayers 4002, 4004, 4006, and 4008, bonded together. The upper surfacesof each of first, second, and third elastomer layers 4002, 4004, and4006 bear uniform serrations 4010 regularly spaced by a distance X thatis much larger than the wavelength of the incident light. Serrations4010 serve to focus the incident light, and may be formed through use ofa micromachined mold as described extensively above. First, second, andthird elastomer layers 4002, 4004, and 4006 function as Fresnel lensesas would be understood of one of ordinary skill in the art.

[0328] Fourth elastomeric layer 4008 bears uniform serrations 4012having a much smaller size than the serrations of the overlyingelastomeric layers. Serrations 4012 are also spaced apart by a muchsmaller distance Y than the serrations of the overlying elastomericlayers, with Y on the order of the wavelength of incident light. suchthat elastomeric layer 4008 flnctions as a diffraction grating.

[0329]FIG. 41 illustrates an embodiment of a refractive structure inaccordance with the present invention which utilizes difference inmaterial refractive index to primarily accomplish diffraction.Refractive structure 4100 includes lower elastomeric portion 4102covered by upper elastomeric portion 4104. Both lower elastomericportion 4102 and upper elastomeric portion 4104 are composed of materialtransmitting incident light 4106. Lower elastomeric portion 4102includes a plurality of serpentine flow channels 4108 separated byelastomeric lands 4110. Flow channels 4108 include fluid 4112 having adifferent refractive index than the elastomeric material making up lands4110. Fluid 4112 is pumped through serpentine flow channels 4108 by theoperation of pump structure 4114 made up of parallel control channels4116 a and 4116 b overlying and separated from inlet portion 4108 a offlow channel 4108 by moveable membrane 4118.

[0330] Light 4106 incident to refractive structure 4100 encounters aseries of uniformly-spaced fluid-filled flow channels 4108 separated byelastomeric lands 4110. As a result of the differing optical propertiesof material present in these respective fluid/elastomer regions,portions of the incident light are not uniformly refracted and interactto form an interference pattern. A stack of refractive structures of themanner just described can accomplish even more complex and specializedrefraction of incident light.

[0331] The refractive elastomeric structures just described can fulfilla variety of purposes. For example, the elastomeric structure could actas a filter or optical switch to block selected wavelengths of incidentlight. Moreover, the refractive properties of the structure could bereadily adjusted depending upon the needs of a particular application.

[0332] For example, the composition (and hence refractive index) offluid flowed through the flow channels could be changed to affectdiffraction. Alternatively, or in conjunction with changing the identityof the fluid flowed, the distance separating adjacent flow channels canbe precisely controlled during fabrication of the structure in order togenerate an optical interference pattern having the desiredcharacteristics.

[0333] 6. Normally-Closed Valve Structure

[0334]FIGS. 7B and 7H above depict a valve structure in which theelastomeric membrane is moveable from a first relaxed position to asecond actuated position in which the flow channel is blocked. However,the present invention is not limited to this particular valveconfiguration.

[0335] FIGS. 42A-42J show a variety of views of a normally-closed valvestructure in which the elastomeric membrane is moveable from a firstrelaxed position blocking a flow channel, to a second actuated positionin which the flow channel is open, utilizing a negative controlpressure.

[0336]FIG. 42A shows a plan view, and FIG. 42B shows a cross sectionalview along line 42B-42B′, of normally-closed valve 4200 in an unactuatedstate. Flow channel 4202 and control channel 4204 are formed inelastomeric block 4206 overlying substrate 4205. Flow channel 4202includes a first portion 4202 a and a second portion 4202 b separated byseparating portion 4208. Control channel 4204 overlies separatingportion 4208. As shown in FIG. 42B, in its relaxed, unactuated position,separating portion 4008 remains positioned between flow channel portions4202 a and 4202 b, interrupting flow channel 4202.

[0337]FIG. 42C shows a cross-sectional view of valve 4200 whereinseparating portion 4208 is in an actuated position. When the pressurewithin control channel 4204 is reduced to below the pressure in the flowchannel (for example by vacuum pump), separating portion 4208experiences an actuating force drawing it into control channel 4204. Asa result of this actuation force membrane 4208 projects into controlchannel 4204, thereby removing the obstacle to a flow of materialthrough flow channel 4202 and creating a passageway 4203. Upon elevationof pressure within control channel 4204, separating portion 4208 willassume its natural position, relaxing back into and obstructing flowchannel 4202.

[0338] The behavior of the membrane in response to an actuation forcemay be changed by varying the width of the overlying control channel.Accordingly, FIGS. 42D-42H show plan and cross-sectional views of analternative embodiment of a normally-closed valve 4201 in which controlchannel 4207 is substantially wider than separating portion 4208. Asshown in cross-sectional views FIG. 42E-F along line 42E-42E′ of FIG.42D, because a larger area of elastomeric material is required to bemoved during actuation, the actuation force necessary to be applied isreduced.

[0339]FIGS. 42G and H show a cross-sectional views along line 40G-40G′of FIG. 40D. In comparison with the unactuated valve configuration shownin FIG. 42G, FIG. 42H shows that reduced pressure within wider controlchannel 4207 may under certain circumstances have the unwanted effect ofpulling underlying elastomer 4206 away from substrate 4205, therebycreating undesirable void 4212.

[0340] Accordingly, FIG. 421 shows a plan view, and 42J across-sectional view along line 42J-42J′ of FIG. 42I, of valve structure4220 which avoids this problem by featuring control line 4204 with aminimum width except in segment 4204 a overlapping separating portion4208. As shown in FIG. 42J, even under actuated conditions the narrowercross-section of control channel 4204 reduces the attractive force onthe underlying elastomer material 4206, thereby preventing thiselastomer material from being drawn away from substrate 4205 andcreating an undesirable void.

[0341] While a normally-closed valve structure actuated in response topressure is shown in FIGS. 42A-42J, a normally-closed valve inaccordance with the present invention is not limited to thisconfiguration. For example, the separating portion obstructing the flowchannel could alternatively be manipulated by electric or magneticfields, as described extensively above.

[0342] 7. Separation of Materials

[0343] In a further application of the present invention, an elastomericstructure can be utilized to perform separation of materials. FIG. 43shows one embodiment of such a device.

[0344] Separation device 4300 features an elastomeric block 4301including fluid reservoir 4302 in communication with flow channel 4304.Fluid is pumped from fluid reservoir 4306 through flow channel 4308 byperistaltic pump structure 4310 formed by control channels 4312overlying flow channel 4304, as has been previously described at length.Alternatively, where a peristaltic pump structure in accordance with thepresent invention is unable to provide sufficient back pressure, fluidfrom a reservoir positioned outside the elastomeric structure may bepumped into the elastomeric device utilizing an external pump.

[0345] Flow channel 4304 leads to separation column 4314 in the form ofa channel packed with separation matrix 4316 behind porous frit 4318. Asis well known in the art of chromatography, the composition of theseparation matrix 4316 depends upon the nature of t32ehe materials to beseparated and the particular chromatography technique employed. Theelastomeric separation structure is suitable for use with a variety ofchromatographic techniques, including but not limited to gel exclusion,gel permeation, ion exchange, reverse phase, hydrophobic interaction,affinity chromatography, fast protein liquid chromatography (FPLC) andall formats of high pressure liquid chromatography (HPLC). The highpressures utilized for HPLC may require the use of urethane,dicyclopentadiene or other elastomer combinations.

[0346] Samples are introduced into the flow of fluid into separationcolumn 4314 utilizing load channel 4319. Load channel 4319 receivesfluid pumped from sample reservoir 4320 through pump 4321. Upon openingof valve 4322 and operation of pump 4321, sample is flowed from loadchannel 4319 into flow channel 4304. The sample is then flowed throughseparation column 4314 by the action of pump structure 4312. As a resultof differential mobility of the various sample components in separationmatrix 4316, these sample components become separated and are elutedfrom column 4314 at different times.

[0347] Upon elution from separation column 4314, the various samplecomponents pass into detection region 4324. As is well known in the artof chromatography, the identity of materials eluted into detectionregion 4324 can be determined utilizing a variety of techniques,including but not limited to fluorescence, UV/visible/IR spectroscopy,radioactive labeling, arnperometric detection, mass spectroscopy, andnuclear magnetic resonance (NMR).

[0348] A separation device in accordance with the present inventionoffers the advantage of extremely small size, such that only smallvolumes of fluid and sample are consumed during the separation. Inaddition, the device offers the advantage of increased sensitivity. Inconventional separation devices, the size of the sample loop willprolong the injection of the sample onto the column, causing width ofthe eluted peaks to potentially overlap with one another. The extremelysmall size and capacity of the load channel in general prevents thispeak diffusion behavior from becoming a problem.

[0349] The separation structure shown in FIG. 43 represents only oneembodiment of such a device, and other structures are contemplated bythe present invention. For example, while the separation device of FIG.43 features a flow channel, load loop, and separation column oriented ina single plane, this is not required by the present invention. One ormore of the fluid reservoir, the sample reservoir, the flow channel, theload loop, and the separation column could be oriented perpendicular toone another and/or to the plane of the elastomeric material utilizingvia structures whose formation is described at length above inconnection with FIG. 35A-D.

[0350] 8. Cell Pen/Cell Cage/Cell Grinder

[0351] In yet a further application of the present invention, anelastomeric structure can be utilized to manipulate organisms or otherbiological material. FIGS. 44A-44D show plan views of one embodiment ofa cell pen structure in accordance with the present invention.

[0352] Cell pen array 4400 features an array of orthogonally-orientedflow channels 4402, with an enlarged “pen” structure 4404 at theintersection of alternating flow channels. Valve 4406 is positioned atthe entrance and exit of each pen structure 4404. Peristaltic pumpstructures 4408 are positioned on each horizontal flow channel and onthe vertical flow channels lacking a cell pen structure.

[0353] Cell pen array 4400 of FIG. 44A has been loaded with cells A-Hthat have been previously sorted, perhaps by a sorting structure asdescribed above in conjunction with FIG. 36. FIGS. 44B-44C show theaccessing and removal of individually stored cell C by 1) opening valves4406 on either side of adjacent pens 4404 a and 4404 b, 2) pumpinghorizontal flow channel 4402 a to displace cells C and G, and then 3)pumping vertical flow channel 4402 b to remove cell C. FIG. 44D showsthat second cell G is moved back into its prior position in cell penarray 4400 by reversing the direction of liquid flow through horizontalflow channel 4402 a.

[0354] The cell pen array 4404 described above is capable of storingmaterials within a selected, addressable position for ready access.However, living organisms such as cells may require a continuous intakeof foods and expulsion of wastes in order to remain viable. Accordingly,FIGS. 45A and 45B show plan and cross-sectional views (along line45B-45B′) respectively, of one embodiment of a cell cage structure inaccordance with the present invention.

[0355] Cell cage 4500 is formed as an enlarged portion 4500 a of a flowchannel 4501 in an elastomeric block 4503 in contact with substrate4505. Cell cage 4500 is similar to an individual cell pen as describedabove in FIGS. 44A-44D, except that ends 4500 b and 4500 c of cell cage4500 do not completely enclose interior region 4500 a. Rather, ends 4500a and 4500 b of cage 4500 are formed by a plurality of retractablepillars 4502. Pillars 4502 may be part of a membrane structure of anormally-closed valve structure as described extensively above inconnection with FIGS. 42A-42J.

[0356] Specifically, control channel 4504 overlies pillars 4502. Whenthe pressure in control channel 4504 is reduced, elastomeric pillars4502 are drawn upward into control channel 4504, thereby opening end4500 b of cell cage 4500 and permitting a cell to enter. Upon elevationof pressure in control channel 4504, pillars 4502 relax downward againstsubstrate 4505 and prevent a cell from exiting cage 4500.

[0357] Elastomeric pillars 4502 are of a sufficient size and number toprevent movement of a cell out of cage 4500, but also include gaps 4508which allow the flow of nutrients into cage interior 4500 a in order tosustain cell(s) stored therein. Pillars 4502 on opposite end 4500 c aresimilarly configured beneath second control channel 4506 to permitopening of the cage and removal of the cell as desired.

[0358] Under certain circumstances, it may be desirable to grind/disruptcells or other biological materials in order to access component pieces.

[0359] Accordingly, FIGS. 46A and 46B show plan and cross sectionalviews (along line 46B-46B′) respectively, of one embodiment of cellgrinder structure 4600 in accordance with the present invention. Cellgrinder 4600 includes a system of interdigitated posts 4602 within flowchannel 4604 which close together upon actuation of integral membrane4606 by overlying control channel 4608. By closing together, posts 4602crush material present between them.

[0360] Posts 4602 may be spaced at intervals appropriate to disruptentities (cells) of a given size. For disruption of cellular material,spacing of posts 4602 at an interval of about 2 μm is appropriate. Inalternative embodiments of a cell grinding structure in accordance withthe present invention, posts 4602 may be located entirely on theabove-lying membrane, or entirely on the floor of the control channel.

[0361] 9. Pressure Oscillator

[0362] In yet a further application of the present invention, anelastomeric structure can be utilized to create a pressure oscillatorstructure analogous to oscillator circuits frequently employed in thefield of electronics. FIG. 47 shows a plan view of one embodiment ofsuch a pressure oscillator structure.

[0363] Pressure oscillator 4700 comprises an elastomeric block 4702featuring flow channel 4704 formed therein. Flow channel 4704 includesan initial portion 4704 a proximate to pressure source 4706, and aserpentine portion 4704 b distal from pressure source 4706. Initialportion 4704 a is in contact with via 4708 in fluid communication withcontrol channel 4710 formed in elastomeric block 4702 above the level offlow channel 4704. At a location more distal from pressure source 4706than via 4708, control channel 4710 overlies and is separated from flowchannel 4704 by an elastomeric membrane, thereby forming valve 4712 aspreviously described.

[0364] Pressure oscillator structure 4700 operates as follows.Initially, pressure source 4706 provides pressure along flow channel4704 and control channel 4710 through via 4708. Because of theserpentine shape of flow channel 4704 b, pressure is lower in region4704 b as compared with flow channel 4710. At valve 4712, the pressuredifference between serpentine flow channel portion 4704 b and overlyingcontrol channel 4710 eventually causes the membrane of valve 4712 toproject downward into serpentine flow channel portion 4704 b, closingvalve 4712. Owing to the continued operation of pressure source 4706however, pressure begins to build up in serpentine flow channel portion4704 b behind closed valve 4712. Eventually the pressure equalizesbetween control channel 4710 and serpentine flow channel portion 4704 b,and valve 4712 opens.

[0365] Given the continuos operation of the pressure source, theabove-described build up and release of pressure will continueindefinitely, resulting in a regular oscillation of pressure. Such apressure oscillation device may perform any number of possiblefunctions, including but not limited to timing.

[0366] 9. Side-Actuated Valve

[0367] While the above description has focused upon microfabricatedelastomeric valve structures in which a control channel is positionedabove and separated by an intervening elastomeric membrane from anunderlying flow channel, the present invention is not limited to thisconfiguration. FIGS. 48A and 48B show plan views of one embodiment of aside-actuated valve structure in accordance with one embodiment of thepresent invention.

[0368]FIG. 48A shows side-actuated valve structure 4800 in an unactuatedposition. Flow channel 4802 is formed in elastomeric layer 4804. Controlchannel 4806 abutting flow channel 4802 is also formed in elastomericlayer 4804. Control channel 4806 is separated from flow channel 4802 byelastomeric membrane portion 4808. A second elastomeric layer (notshown) is bonded over bottom elastomeric layer 4804 to enclose flowchannel 4802 and control channel 4806.

[0369]FIG. 48B shows side-actuated valve structure 4800 in an actuatedposition. In response to a build up of pressure within control channel4806, membrane 4808 deforms into flow channel 4802, blocking flowchannel 4802. Upon release of pressure within control channel 4806,membrane 4808 would relax back into control channel 4806 and open flowchannel 4802.

[0370] While a side-actuated valve structure actuated in response topressure is shown in FIGS. 48A and 48B, a side-actuated valve inaccordance with the present invention is not limited to thisconfiguration. For example, the elastomeric membrane portion locatedbetween the abutting flow and control channels could alternatively bemanipulated by electric or magnetic fields, as described extensivelyabove.

[0371] 10. Additional Applications

[0372] The following represent further aspects of the present invention:present valves and pumps can be used for drug delivery (for example, inan implantable drug delivery device); and for sampling of biologicalfluids (for example, by storing samples sequentially in a column withplugs of spacer fluid therebetween, wherein the samples can be shuntedinto different storage reservoirs, or passed directly to appropriatesensor(s). Such a fluid sampling device could also be implanted in thepatient's body.

[0373] The present systems can also be used for devices which relieveoverpressure in vivo using a micro-valve or pump. For example, animplantable bio-compatible micro-valve can be used to relieveover-pressures in the eye which result from glaucoma. Other contemplateduses of the present switchable micro-valves include implantation in thespermatic duct or fallopian tube allowing reversible long-term orshort-term birth control without the use of drugs.

[0374] Further uses of the present invention include DNA sequencingwhereby the DNA to be sequenced is provided with a polymerase and aprimer, and is then exposed to one type of DNA base (A, C, T, or G) at atime in order to rapidly assay for base incorporation. In such a system,the bases must be flowed into the system and excess bases washed awayrapidly. Pressure driven flow, gated by elastomeric micro-valves inaccordance with the present invention would be ideally suited to allowfor such rapid flow and washing of reagents.

[0375] Other contemplated uses of the present micro-valve and micro-pumpsystems include uses with DNA chips. For example, a sample can be flowedinto a looped channel and pumped around the loop with a peristalticaction such that the sample can make many passes over the probes of theDNA array. Such a device would give the sample that would normally bewasted sitting over the non-complimentary probes the chance to bind to acomplimentary probe instead. An advantage of such a looped-flow systemis that it would reduce the necessary sample volume, and therebyincrease assay sensitivity.

[0376] Further applications exist in high throughput screening in whichapplications could benefit by the dispensing of small volumes of liquid,or by bead-based assays wherein ultrasensitive detection wouldsubstantially improve assay sensitivity.

[0377] Another contemplated application is the deposition of array ofvarious chemicals, especially oligonucleotides, which may or may nothave been chemically fabricated in a previous action of the devicebefore deposition in a pattern or array on a substrate via contactprinting through fluid channel outlets in the elastomeric device inclose proximity to a desired substrate, or by a process analogous toink-jet printing.

[0378] The present microfabricated elastomeric valves and pumps couldalso be used to construct systems for reagent dispensing, mixing andreaction for synthesis of oligonucleotides, peptides or otherbiopolymers.

[0379] Further applications for the present invention include ink jetprinter heads, in which small apertures are used to generate a pressurepulse sufficient to expel a droplet. An appropriately actuatedmicro-valve in accordance with the present invention can create such apressure pulse. The present micro-valves and pumps can also be used todigitally dispense ink or pigment, in amounts not necessarily as smallas single droplets. The droplet would be brought into contact with themedium being printed on rather than be required to be fired through theair.

[0380] Yet other uses of the present systems are in fluidic logiccircuits which offer the advantages of being useable in radiationresistant applications. A further advantage of such fluidic logiccircuits is that, being non-electronic, such fluidic logic circuitry maynot be probed by electro magnetic sensors, thus offering a securitybenefit.

[0381] Yet further uses of the present invention would take advantage ofthe ready removal and reattachment of the structure from an underlyingsubstrate such as glass, utilizing a glass substrate patterned with abinding or other material. This allows separate construction of apatterned substrate and elastomer structure. For instance, a glasssubstrate could be patterned with a DNA microarray, and an elastomervalve and pump structure sealed over the array in a subsequent step.

[0382] 11. Additional Aspects of the Invention The following representfurther aspects of the present invention: the use of a deflectablemembrane to control flow of a fluid in a microfabricated channel of anelastomeric structure; the use of elastomeric layers to make amicrofabricated elastomeric device containing a microfabricated movableportion; and the use of an elastomeric material to make amicrofabricated valve or pump.

[0383] A microfabricated elastomeric structure in accordance with oneembodiment of the present invention comprises an elastomeric blockformed with microfabricated recesses therein, a portion of theelastomeric block deflectable when the portion is actuated. The recessescomprise a first microfabricated channel and a first microfabricatedrecess, and the portion comprises an elastomeric membrane deflectableinto the first microfabricated channel when the membrane is actuated.The recesses have a width in the range of 10 μm to 200 μm and theportion has a thickness of between about 2 μm and 50 μm. Themicrofabricated elastomeric structure may be actuated at a speed of 100Hz or greater and contains substantially no dead volume when the portionis actuated.

[0384] A method of actuating an elastomeric structure comprisesproviding an elastomeric block formed with first and secondmicrofabricated recesses therein, the first and second microfabricatedrecesses separated by a membrane portion of the elastomeric blockdeflectable into one of the first and second recesses in response to anactuation force, and applying an actuation force to the membrane portionsuch that the membrane portion is deflected into one of the first andthe second recesses.

[0385] A method of microfabricating an elastomeric structure inaccordance with one embodiment of the present invention comprisesforming a first elastomeric layer on a substrate, curing the firstelastomeric layer, and patterning a first sacrificial layer over thefirst elastomeric layer. A second elastomeric layer is formed over thefirst elastomeric layer, thereby encapsulating the first patternedsacrificial layer between the first and second elastomeric layers, thesecond elastomeric layer is cured, and the first patterned sacrificiallayer is removed selective to the first elastomeric layer and the secondelastomeric layer, thereby forming at least one first recess between thefirst and second layers of elastomer.

[0386] An alternative embodiment of a method of fabricating furthercomprises patterning a second sacrificial layer over the substrate priorto forming the first elastomeric layer, such that the second patternedsacrificial layer is removed during removal of the first patternedsacrifical layer to form at least one recess along a bottom of the firstelastomeric layer.

[0387] A microfabricated elastomeric structure in accordance with oneembodiment of the present invention comprises an elastomeric block, afirst channel and a second channel separated by a separating portion ofthe elastomeric structure, and a microfabricated recess in theelastomeric block adjacent to the separating portion such that theseparating portion may be actuated to deflect into the microfabricatedrecess. 66. Deflection of the separating portion opens a passagewaybetween the first and second channels.

[0388] A method of controlling fluid or gas flow through an elastomericstructure comprises providing an elastomeric block, the elastomericblock having first, second, and third microfabricated recesses, and theelastomeric block having a first microfabricated channel passingtherethrough, the first, second and third microfabricated recessesseparated from the first channel by respective first, second and thirdmembranes deflectable into the first channel, and deflecting the first,second and third membranes into the first channel in a repeatingsequence to peristaltically pump a flow of fluid through the firstchannel.

[0389] A method of microfabricating an elastomeric structure, comprisingmicrofabricating a first elastomeric layer, microfabricating a secondelastomeric layer; positioning the second elastomeric layer on top ofthe first elastomeric layer; and bonding a bottom surface of the secondelastomeric layer onto a top surface of the first elastomeric layer.

[0390] While the present invention has been described herein withreference to particular embodiments thereof, a latitude of modification,various changes and substitutions are intended in the foregoingdisclosure, and it will be appreciated that in some instances somefeatures of the invention will be employed without a corresponding useof other features without departing from the scope of the invention asset forth. Therefore, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from the essential scope and spirit of the presentinvention. It is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments and equivalents falling within the scope of the claims.

[0391] Incorporated herein as part of the present specification is theentire contents of Appendix A, “Monolithic Microfabricated Valves andPumps by Multilayer Soft Lithography”, Unger et al., Science, Vol. 288,pp. 113-116 (Apr. 7, 2000), which appears herein before the claims andwhich is to be construed as part of the present specification for allpurposes.

What is claimed is:
 1. A method of microfabricating an elastomericstructure, comprising: microfabricating a first elastomeric layer;microfabricating a second elastomeric layer; positioning the secondelastomeric layer on top of the first elastomeric layer; and bonding abottom surface of the second elastomeric layer onto a top surface of thefirst elastomeric layer.
 2. The method of claim 1 wherein the first andsecond elastomeric layers are microfabricated by replication molding. 3.The method of claim 1 wherein the first and second elastomeric layersare microfabricated by sacrificial layer methods.
 4. The method of claim1 wherein the first and second elastomeric layers are microfabricated byinjection molding.
 5. The method of claim 1 wherein: the firstelastomeric layer is fabricated on a first micromachined mold having atleast one raised protrusion which forms at least one recess in thebottom of the first elastomeric layer; and the second elastomeric layeris fabricated on a second micromachined mold having at least one raisedprotrusion which forms at least one recess in the bottom of the firstelastomeric layer
 6. The method of claim 1 further comprising:sequential addition of further elastomeric layers, whereby each layer isadded by: microfabricating a successive elastomeric layer; and bondingthe bottom surface of the successive elastomeric layer onto a topsurface of the elastomeric structure.
 7. The method of claim 1 whereinthe first elastomeric layer has an excess of a first chemical speciesand the second elastomeric layer has an excess of a second chemicalspecies.
 8. The method of claim 7 wherein the elastomeric layerscomprise thermoset elastomers which are bonded together by heating abovean elastic/plastic transition temperature of at least one of the firstand second elastomeric layers.
 9. The method of claim 7 wherein thefirst chemical species forms bonds with the second chemical species whenat least one chemical species is activated.
 10. The method of claim 7wherein the first and second elastomeric layers are composed of the samecomponent materials, but differ in the ratio in which the componentmaterials are mixed together.
 11. The method of claim 1 wherein thefirst and second layers are bonded by a layer of adhesive.
 12. Themethod of claim 1 wherein at least one of the elastomeric layers furthercomprises a conductive portion.
 13. A method of microfabricating anelastomeric structure, comprising: forming a first elastomeric layer ona substrate; curing the first elastomeric layer; patterning a firstsacrificial layer over the first elastomeric layer; forming a secondelastomeric layer over the first elastomeric layer, therebyencapsulating the first patterned sacrificial layer between the firstand second elastomeric layers; curing the second elastomeric layer; andremoving the first patterned sacrificial layer selective to the firstelastomeric layer and the second elastomeric layer, thereby forming atleast one first recess between the first and second layers of elastomer.14. The method of claim 13 further comprising patterning a secondsacrificial layer over the substrate prior to forming the firstelastomeric layer, such that the second patterned sacrificial layer isremoved during removal of the first patterned sacrifical layer to format least one recess along a bottom of the first elastomeric layer. 15.The method of claim 13 further comprising: patterning a secondsacrificial layer over the second elastomeric layer; forming a thirdelastomeric layer over the second elastomeric layer, therebyencapsulating the second patterned sacrificial layer between the secondand third elastomeric layers; and curing the third elastomeric layersuch that the second patterned sacrificial layer is removed duringremoval of the first patterned sacrifical layer to form a recess betweenthe second and third elastomeric layers.
 16. The method of claim 13further comprising: patterning an (n−1)th sacrifical layer over the nthelastomer layer; forming a (n+1)th elastomeric layer over the (n−1)thpatterned sacrifical layer; and bonding the bottom surface of the(n−1)th elastomeric layer onto a top surface of the nth elastomericlayer thereby encapsulating the (n−1)th patterned sacrificial layerbetween the nth and (n+1)th elastomeric layers; and curing the (n+1)elastomeric layer such that the (n−1)th patterned sacrificial layer isremoved during removal of the first patterned sacrifical layer to form arecess between the nth and (n+1)th elastomeric layers.
 17. The method ofclaim 13 wherein the first patterned sacrificial layer comprisesphotoresist.
 18. The method of claim 14 further comprising bonding thefirst elastomeric layer to the second elastomeric layer.
 19. The methodof claim 18 wherein the bonding occurs by interpenetration and reactionof the polymer chains of the uncured elastomer with the polymer chainsof the cured elastomer.
 20. The method of claim 18 wherein the firstelastomeric layer has an excess of a first chemical species and thesecond elastomeric layer has an excess of a second chemical species. 21.The method of claim 18 wherein the first chemical species forms bondswith the second chemical species when at least one chemical species isactivated.
 22. The method of claim 18 wherein the first and secondelastomeric layers are formed of different elastomeric materials.